Actually I don't think he could, unless she found the tunnel that led to the prison itself.  He could make everyone feel uncomfortable, but he couldn't do anything that would reveal what was really there.  Hey even the Denarians didn't seem to know what was really on the island in Small Favor. Heck if Harry had fully understood what he had done and what power that gave him on the island, Shaggy wouldn't have been able to do squat.  As it was, though Harry suddenly was aware of everything, until Alfred taught him he wasn't aware of his control.

This shouldn't be all that difficult to comprehend.  The Council is corrupt and falling apart. As dangerous as Harry might be there are factions pulling in multiple directions. To do this they had to act when members of the Senior Council were sidelined to make it work. There are at least two cabals in motion.  Jim is guiding us into a wizard civil war.  Chicago is going to be the rally point for the rebellion.He doesn't need to tell Alfred anything. It's a demon supermax.  To Alfred your guilty if you come around, he just hasn't killed you yet.

   Didn't talk to Ivy?  Yes, I understand she is totally into her Archive role now, but she is still Ivy.  I
believe that Ivy still sees Harry as a friend.  What I thought was weird, he didn't even give her
a head nod in acknowledgement or vice versa..

  In Battle Ground, Harry clearly talks about the six months Mab stayed on Demonreach, "to keep me alive," while his soul did it's walk about.  Now that was Uriel's idea, if Mab had had her way, he might have woken up as soon as she got him to dry land. Then who knows?  She might of killed him for trying to evade her by trying to kill himself.

I don't think Murphy will be back, and if she does I think you will find her totally changed from what she was.

I do see her coming back eventually -- see my prediction a page or two ago -- but not for a while.

Harry doesn't have to kill an immortal to take on a mantle. There's one mantle mentioned in BG that we know has been passed around: Kringle. The Erlking might have been offended by the joke, but it's also the only mantle (that i remember) which has been mentioned as being kind of supplemental, and not a major mantle.

Ivy too, probably.