Wow, some of you have some very vivid imaginations. As for myself, I only hope that certain things will not happen. I have read a whole lot of fantasy and sci-fi books and most seem to have the same sort of endings when this kind of situation is presented. I just hope she doesn't use this "generic ending" which I have seen countless times.

This ending usually involves the spy character performing some heroic deed which causes our beloved hero to win, but also results in the death of said spy. Aside from the fact that I am a Snape fan, I really am tired of reading this particular scenario. (Besides, Snape does not do the whole blatant self-sacrificial hero type stuff.)

Now if I were to seriously predict what I believe will happen...I think that Snape will still serve as a spy and saboteur within Voldemort's ranks. Snape will be passing information along by either someone in the Order who finds the truth about Dumbledor's death or through a couple of portraits of Dumbledor (one at Hogwarts and one hidden away by Snape.) Through this information, Harry will be able to find the remaining Horcruxes and destroy them, except Nagini. I agree with Psyduck that Snape will probably kill the snake, simply because he is in the best position to do so.

As for which characters I think will bite the big one: One is certainly Voldemort. The other is entirely up for grabs, depending on what Ms Rowling considers "main."