Given that in my game, all kinds of people tied themselves to a player that didn't show up, it's not a big deal.  They still have connections through the absent third party.

Also the early scenes might have some connection with the absent player, based on what some of the PCs have learned so far.

Let the guest star in any story, or with any interesting NPC that has been important in the stories.  Somebody getting hospitalized, for example, is a great excuse for a PC relative to show up...(or I guess killed too...at the funeral instead of the hospital waiting room)

And yeah.  They can develop aspects in play too....but aspects actually do help tie in newbies to an established group, so it's helpful to the GM if the players make at least a little effort along those lines.

Funny you should mention Fringe.  I always thought it was the best Mage: The Awakening campaign ever set to television.  You just have to realize that most of the protagonists are in fact mages, whether or not they realize it.  By the later seasons it's increasingly obvious (eg, the FBI agent's background....).  All sorts of things in that show work pretty much exactly like they would in a Mage game, including different paradigms for different characters and the consensus reality being stressed by "magic" and hitting back.

This attitude might be because the longest running Mage game I played had a bunch of my friends as mid-20-somethings after college graduation literally awakening as mages..and by the time we had any power we had each evolved our own ideas of what magic was, independent of all the established power structures.  I'm not sure I'd have the same impression of Fringe if my Mage game had involved all of us being brought up by, say, the Technocracy or Sons of the Ether.

But yes, Fringe works pretty well in Fate too.  Most forms of public entertainment do, and it isn't an accident.  Fate is written by a bunch of ex-Amber RPG players who were unsatisfied with how that system dealt with conflict.  Amber was designed to simulate a science-fiction/fantasy story arc.  These authors were fans of written stories, TV stories, movies, had been exposed to a lot of RPG and took a lot of good ideas from them.  But it was deliberately based around the idea of the protagonist in a story, and having the game mechanics work the way stuff does in a story.  A protagonist loses so that rising from the ashes is more dramatic.  I can't think of the last story I read or saw where bad things and outright defeats didn't happen to the protagonists.

Stories generally aren't written like a d20 game, where the protagonists go from one encounter to another, of varying degrees of challenge but never really experiencing more than severe resource-depletion and needing to rest from time to time.  D20, and 1st edition D&D before it came out of wargaming roots, where what is going on is the GM is presenting a challenge and the fun is overcoming the challenge, more like a CRPG than a novel.  There are genre conventions (eg, Champions/Hero Games are organized in a similar way, except that the genre allows PCs to lose without getting killed, hence deathtraps and the like) but the basic pattern is similar.  The GM isn't expected to present a challenge that the PC's are likely to lose most of the time.  The roleplaying is both there to make you care more about the challenges and also to provide an extra layer of social complexity to some obstacles.  But mostly it's to make you care.

Stories don't work like that, and it is a hard adjustment to people used to one style switching to the other.

Seems to me the debt would be tied more to having less of your soul to work with, and whatever you think the consequences of that might be.

For Harry, this initially expressed as a numb hand when he did a hand-force-evothaum, and likely also in a desire to do more "soul regenerating" stuff, as in his relationship with Luccio.

In a lot of ways Soulfire in the books is skinned as a lesser form of the death curse.  You could skin that as being more likely to be ruled by your aspects, but Harry seems to see it as something that risks his life in a way similar to how firing your memories of fire at people as a ghost is risky.  After the first book he's more careful with it, so we don't tend to see him piling up "soulfire" debt.   If I was playing a soulfire based character, I'd likely go down the road of debt being consequences of an incomplete or damaged soul, and think about what using certain kinds of magic would translate into.

Harry mostly uses soulfire with his fire spells, primarily to beat the catch on critters vulnerable to faith.  This use seems mostly to make him more aggressive or inclined to gloat/victory dance (think about how he behaved in Changes when chasing the vampires in the first scene).  This might be because he tends to throw fear/rage at enemies with fire, and with less of that in his system he behaves more like a fight is a game or contest.  When he made a hand construct, his hand went numb, which is pretty obvious.  When he's used it to reinforce defensive spells I've not noticed anything in particular, but maybe Jim's doing something subtle or I'm off base entirely   Mostly though I think Harry got a lot more careful when he realized he's throwing his soul at people so he hasn't been getting into a lot of situations where he incurs debt to it as a solution.

The goal is to make all options entertaining, success or failure.  Failure just leads to deeper stories.

The problem in a game like DFRPG is that the opposition ranges from a plain, ordinary thug or police or bystander who doesn't understand to literal gods.

It's a thing in this series, a lot of why the stories are entertaining, to have opposition, older, wiser, more powerful and beat them anyway.  But you don't get that level of satisfaction without earning it.   Cowl isn't Cowl because he scared Harry the first time he met.  He's Cowl because Harry foiled his plans and every time they've met again, Cowl's avoided direct confrontation and STILL nearly killed Harry, plus accomplished something, even if not his primary goals.   Marcone's picked a different arc.  Mavra a third.  Nicodemus a fourth.

The sign you are on the right track is when players are emotionally engaged in the bad guy.  Marcone's become a frenemy, a much more interesting outcome than Harry blasting him to ash after he "lost" a soulgaze in the first book.  Harry never got Cowl, but Cowl's so badass that his "minions" are all at about Harry's weight, so he got the satisfaction of getting the other Kemmlerites the first time, the White Court (cripes, most of its leadership) the second time and Peabody the third time.   Mavra's an example where the GM maybe pushed it too far, and having her permanently exit the game in favor of the Nickleheads was a good move.  There was no way to make Mavra's conflict more interesting, Harry's final threat was convincing - it was the player saying he'd make a campaign altering move, possibly ending move, if he saw her again, just to kill her.   The Denarians, by contrast, again have tiers of opposition - we go from merely foiling the plan and defeating one of the minions to pretty much wiping out all of the second tier and perma-killing one or two of their most dangerous human hosts to, well, spoilers.   That story isn't over, and it looks like it may be Michael's story more than Harry's anyway.

This is why I wanted the corpse-swap trick to be an important plot point.  The PC's have advanced against the Kemmlerite in an important way when they force that tactic.  It's a reveal as big as when Cowl and the ghouls got called in, or when Peabody was revealed at the trial.  Changes the whole nature of the conflict, so the players should feel some accomplishment even if the big bad gets away to return someday....even gives  them some hooks on how to go after the Kemmlerite instead of just reacting.

The Red Court plot, by contrast, is an attempt to set up a Marcone-like situation with a side of venom addiction.  Since the path to freedom is clear (live a righteous life) and that's a primary conflict of the character, the player signed up for this kind of plot (just as the White Council player with a temptation of power trouble signed up to be tempted and manipulated by his desires, much as Harry was).

You can do a whole story or campaign without super-competent opposition.  But if you're going to bring in the nobility of the Red or White courts, black court that are old enough to have survived the purges, first generation Kemmler disciples, or non-thug Denarians, your players are going to EXPECT them to be super-competent and be just as let down if behave like a street-corner thug in planning and preparation.  The primary difference between a recurring villain and one that's just there to show how awesome the PC's are and is forgotten the next day is the former knows when to concede or retreat, and does it MUCH earlier.  Give PCs enough time in a fight and they'll win.  Also in DFRPG, losing isn't what it is in other games.  If you miscalculate and your super-competent NPC wins, presumably the PCs were formidable enough to earn respect and then you go with the recruitment offers, or the using them as bait to draw in others, etc, something that furthers the story.     

Hell, losing is a heck of a way to learn about the opposition.  DFRPG greatly supports that trope, if the player's ok with bad things happening to his character before being rescued or escaping somehow.  Seriously, Harry's player has a very strong stomach for that, more than most people.   The game won't work as well if PC's aren't willing to concede sometimes, and GMs are encouraged to show the way by having their bad guys concede, to show it isn't the end of the world.

Ok.  Your Kemmlerite needs to be in the room with the WC wizard to get the maximum payoff (blood).  If you're a body switcher, the obvious last ditch escape plan is to have another person within line of sight when you take the big risk, or  hell, better, have their hair or something which lets you switch when they aren't even in the room. 

If the WC wizard reacts badly to the attempt to get blood, and it looks like he'll do something you can't easily talk yourself out of or escape by other means. swap with the other body, while he's threatening/interrogating the poor schmuck that is now inside your former body.

Totally in character, totally fair.  If you escape by more normal means (talking your way out, physically escaping, winning a throwdown) fine and good, but if the wizard gets the better of you, his big reward is learning that you're a body-switcher, assuming he doesn't just kill the poor schmuck you swapped with (he probably won't, as you are mortal too, hence lawbreaker but he could have a gun or knife or something).

So you've got 3 conditions, all interesting.  1, you get the blood and Plan A is in operation, 2, you don't but manage to escape via physical or social talents that don't give anything away, and maybe pushed him into a little necromancy trying to stop you 3, you are forced to resort to your emergency body-swap spell (preferably done as an enchanted item or potion to make it nearly impossible to prevent without foreknowledge of such a power) and he learns you can DO that.  So now he knows if he really wants to stop you he'll have to have to shut that down...which again might tempt him into necromancy as an obvious counter.  Plus he has to be paranoid about anyone he encounters, because it might be you.

Plus a bunch of other options where he ends up willingly going to the dark side and working with your necromancer, just cause he wants the power or is convinced via social interaction.

From what you say though, my Kemmlerite should have at least 2, if not more, contingency plans in place to ensure that even if he can't seduce the White Council PC into necromancy, that he can still complete his ritual, and if not that, have a couple plans for escape.

This sort of planning is most important on really long lived folks who also have experienced a lot of life and death situations.  So Mavra, a rare black court survivor, is shown as thinking really hard about Dresden when her scourge comes to town.  She fills the place with mortals, arms them with a variety of things difficult to defend against, puts out a decoy to "die" and actually spends the whole fight veiled and upstairs, taking pictures, so all the really destructive things that occur downstairs don't touch her AND she learns even more about Dresden and his allies - which she uses later to get her hands on Kemmler's book and eliminate anybody but Dresden who might have read it....

That's a very convincing portrayal of an intelligent survivor, maximizing her own abilities and limiting the scope of her enemies, using mostly resources she doesn't care about.

So if your Kemmlerite is somebody like that, someone who survived perhaps the White Council war on his former master and the hunting down of disciples, he's not going to try to seduce a White Council wizard without a damn good backup plan.

OTOH, there has to be a pretty big payoff to risk involving a WC wizard, so his alternative to do the darkhallow-thingie must either also be hazardous or it'll be less effective or, if neither, he's getting big fate point compulsions from aspects to involve THAT wizard in spite of an adequate alternative....in which case he'll be doing the alternative with a big wad of fate points in hand if the WC wizard does try to interfere.

At a bare minimum, his escape plan should be solid, or it isn't credible that he survived this long.  A perfectly adequate precaution is to not seduce the WC wizard in person.  The simple expedient of a phone call, or a letter writing campaign helps quite a bit, although they have the downside of being liable to interception, so maybe the mail drops off a stone and ritual instructions for the communication spell.  Or you work through surrogates that you can afford to lose, etc.   A WC wizard is mostly dangerous in line of sight, or with a connection to you that you don't know about.   Don't do the seduction with either of those things available (if using a ritual stone for communication, rig it so if very much power goes through it fries the connection, etc).

Now to kill two birds in one stone, have your flunkies be signaled when the WC wizard contacts you, so while you're doing the "come to the dark side" seduction, your minions are doing the apartment complex raids etc....ensuring that wizard won't interfere with minions not up to his weight class.

Red court noble has another problem - they tend to be long lived and cunning.  Again, best way to deal with a Fist of Yahweh is to introduce the venom while you are nowhere near the situation.  Spike his drink or his food, or send some flunky who has displeased you to try to introduce the venom addiction....I'm dubious that the venom would work very well on a True Faith type character given red court catch, but maybe the Noble's trying under the principle of "you never know until you try".

One payoff for clever PC actions is to maybe get in the same room with either of the manipulators to force a physical confrontation, where normally neither would get caught out that way.   Eg, the WC wizard insists on personal instruction out of a claimed fear of wardens and an insufficient skills with magical detection and veils to ensure privacy without his "mentor" helping, then sets up some kind of ambush.   The Kemmlerite then might enter a hornet nest of PC nastiness, but still should have a lot of routine items/potions/thaumaturgical aspects and basic all purpose escape and combat plans for ambushes.....I dislike "he escapes in black box text" type fiat ambush failures...I want it to fit the mechanics of the game.  DFRPG/Fate is easier than most because of the concession mechanic, but it still works better if everyone can believe their character would fail to catch the bad guy via the rules of the game, however expressed.

What I have found satisfying is when somebody like that has a realistic set of contingencies for an ambush, ANY ambush, not just the PC's (just look how much better Dresden got after a few years at war).   If caught in an ambush, a character like that doesn't fight.  He runs (see Nicodemus, pretty much always when at a disadvantage).  If the PCs have a really, really good plan, maybe they learn some cool new tricks for their own use later, and if they can compel the right aspects they might be able to keep the person in one place long enough to take them down...but it should feel like a hell of an accomplishment, and PC's should end the fight feeling like the dog that caught the wildcat...

The way Binder works in the books, is that he can have as many summons as he wants out of combat (he summons pretty quickly) to some limit likely based on skills/focus items/etc or even more likely by high concept or other aspect, but in combat he summons one dude per exchange.

That doesn't look like Evothaum to me at all.  That looks like plain old Rituals, where he's just banging out a whatever level of shifts he can generate based on his conviction, complexity based on his skills, without fussing with circles, declarations, blah blah blah.

Just give him rituals, decent conviction, decent lore, focus items to boost both so each exchange he can pop out a dude for a scene and call it done.  You don't get tired with rituals if you don't burn power higher than your conviction.  He can always burn some mental stress and tag an aspect or something if he wants to bang out more than one guy per exchange.

I've always had an issue with convention games and fate - the aspects are so personal and important to the character that I find it hard to pick up a pregen and do much with it - I actually had an easier time working with consequences taken in play than anything on the sheet.

This is probably a personal flaw...other folks may be fine with pregens in DFRPG, but the way I've handled this problem as a GM at a convention in games with similar issues is to find a scenario where people could bring in their favorite characters, perhaps reskinned to a certain power level  (eg, Chest Deep in DFRPG,  60 years old in Ars Magica, 8th level in Pathfinder or 3.5 D&D) and have it be ok. 

You have to have a scenario that provides a strong hook to involve diverse characters, and that doesn't depend on any particular character type or build to succeed (this is actually easier in Fate type games than most).  As a GM you also need to have a high degree of confidence in your ability to manage table variation - you may not agree with the cost of a catch or something but I've found it's best to just trust players - if you extend trust most won't abuse it and those that will are going to likely be disruptive in some other way anyway.

The largest issue with running any Fate game this way is that players need to be better at drawing their aspects to your attention.  OTOH, they will...these are their favorite characters, sometimes with years of history.  My biggest issue GMing fate is keeping track of all the aspects, and not having to remember the players very well is actually a benefit.

DFRPG is a shared world, so it's not hard to imagine a team-up between characters from different "cities" (campaigns), and the never-never allows for inclusion of even alternate reality versions if you need to.   Fate Core or FAE, being genre-neutral would need some mechanism like "the locals tried to summon the greatest avatars of law from space and time...and unfortunately for them, they ended up with you guys" to allow some concepts to be at the same table.  (in that game, which just used a homebrew system to approximate the characters on the fly we had a Judge from the Judge Dredd universe, a Lensman, a Pendragon knight (they had power of high and low justice), a pulp hero lawyer similar to the Doc Savage aid Ham, a Legion of Superheroes character...you get the idea...players built their characters in play based on what in Fate would be their high concept, but pulled them from strong external sources so most of the table could accept what they could or could not do)