JK recently said (on Jonathan Ross?) that she MIGHT continue the story years and years from now, so killing Harry would seriously mess up her ideas... (if he was dead and she carried on, she couldn't call them "Harry Potter" books anymore, but just books set in the same world)
I had theory when I read HBP that the pheonix was important. Authors these days don't tend to fill pages with useless events. It's nearly all relevant.
I don't think Snape is evil still. I think he knows something that we don't...
(He's my favourite character just because of the actor in the films
)
As for people dying, it's most likely going to be Snape and Voldemort to go in this one.
This is just a theory but:
To come back as a ghost, you have to have left some kind of mark (or impression) on the world. Harry looks like his father (but with his mother's eyes
), meaning that they might play an important part in the next book? It might also be a way for Dumbledore to come back and run Hogwarts as a (the first) ghost headmaster
/ 
