Oh, this is beautiful. Bitter, painful, beautiful, and layered. I adore it. Is there any way I can beg, bribe, or blackmail you to stay in the HP mindset for a while longer? (I can offer up the name of an Alan Rickman movie you have not yet seen - try "Blow Dry" with Bill Nighy nd Natasha Richardson.)

I wouldn't worry too much about the canon issues; even aside from the book/movie canon divergences and the slight canon paradoxes in the books, canon's a bit vague on what the adults do for most of the books. Dumbledore's left the castle as far as anyone knows, but the Headmaster's office has sealed itself off and they're communicating with him somehow, and Snape always seems to be able to find the guy for Very Important Conversations In Flashback. No reason you can't assert he's popping back for the odd visit.