Double post.  If you want to be "game-y", you can do this: separate your powers between two item.  One big obvious one with 1 refresh worth of powers: golden lasso that has incite effect: physical blocks.

Then Take bracers (which can be hidden under a jacket) and load them up with powers: Speed, toughness etc...

Since you only get the rebate once regardless of how many items you have, you get the +2 rebate for the lasso.  If you lose the lasso, you only lose 1 refresh worth of powers.

In regards to actions that so not align with a sponsor:  it's easily covered with compels.  If you want to do something with sponsored magic that doesn't meet with the agenda, it simply won't work.  Here's a FP, you can't use it for this scene.

If you have a FP , your sponsor gives you a pass, but if you can't  afford to pay it off, then you are out of luck. 

Not sure the best way to dealing with revoking powers.  If you are doing things against your sponsors agenda enough that you are getting lots of compels, it probably means something is happening in the game, story-wise,  that will justify droppping it at a milestone.

By YS287, every spell must align with the agenda of the sponsor. If that agenda no longer has a place for you in it, the GM should give you your Refresh back.

Losing Powers isn't really covered by the rules, so you could call the Refresh refund a houserule, but I think it's kind of a no-brainer.

Bear in mind, by the way, that characters don't really buy things with Refresh. Players do. Refresh isn't real in-story, except as a very loose representation of how much freedom someone's got.

Sainthood is a specific Catholic institution. And you have to die to become one. So no to the last question.

Paranet Papers updated the Soulfire rules. Now, instead of debt, you get an extra stress track that you can draw on for a little extra power. The lack of debt is part of what makes me think that they can't revoke Soulfire.

That being said, I vaguely recall a WoJ that Hellfire and Soulfire are different takes on the same thing. So maybe your Soulfire will become Hellfire if you become a sufficiently bad person.

Though I note that's a *LOT* of different powers in-play;  IIRC not even Dresden himself had simultaneous access to Hellfire and Soulfire!  I'd be Doylistically worried that all these heavy-duty obligations might result in MOST of his time being spent on the agendas & conflicts of those other Powers, and less on his own agendas & motivations.

Faeries like those bargains, favor-for-service.  Occasionally, it even works out well for the mortal involved... although the further up the Fae food-chain you go, the less likely it becomes that a bargain will seem like "a good idea" (or even "not a horrible idea") by the time you're done!

Pixies?  A bargain a day keeps trouble at bay!
Faerie nobles?  Oh CRAP, what did I do??!?

The only "bargain" that Hell is interested in is the one that gets them your soul (or some sort of access to it, e.g. part of your True Name; or you doing (or permitting) something likely to tempt/corrupt you or another person), and as Burke noted The only thing necessary for the triumph of evil is for good men to do nothing, so taking a "deal" to just do "nothing" can be effectively a complicit action.

Heaven... apparently doesn't MAKE that kind of bargain, or demand those kinds of services.  They got that ineffable thing goin' on.
 They apparently nudge the "right person for the job" in the direction of "a job that needs doing," and just MAYBE if they see you're doing a Good job (note the cap-G) you end up with Soulfire or some other sort of "reward".  But -- being ineffable and all -- their Reward is one likely to be useful in other Heavenly endeavors and/or to end up doing Heaven's Work in other ways.  They're ruddy bastards that way!