Hm, I'd actually hate it if Sirius turned out to be
anything else but dead. Not that I didn't like him or didn't find his death sad, but unnecessary deaths are what happens in a war, bringing him back would be...well, cheesy.
I'd hate it
-if Voldemort was redeemed
-if Hermione's last words were "Oh Viktor, please, don't write Hermione with three n on my gravestone!"
-if Voldemort and the ministry were conspiring, closed Hogwarts, abducted Hermione into the Arctic, Harry went to rescue her, accidentally destroyed their secret base, then Hogwarts's reopened. (Though 'Harry Potter: Fight the Future' would make a cool title
)
-if Harry defeated Voldemort, but found out he carried his offspring and killed himself in self-sacrifice...(Though of course he will be cloned, I'm already looking forward to Harry Potter 9: Voldie vs. Predator)
Sorry, just kidding of course. I 'borrowed' those options from other sources...