Prediction:
Both Voldermort and Snape will die. Harry will probably live.
Spoilers/reasoning
Snape is a very ambiguous character. However...
Voldermort can't be killed without inside help, or a deus-ex-machina. The logical person to provide this help is Snape. Snape needs to gain you-know-who's confidence before he can effectively backstab him. Dumbledorf knew this all along, and was willing to sacrifice himself to put Snape in the proper position, in the belief (possibly only the hope) that Snape will do the right thing.
I don't know what the determining factor in Snape's motivation is going to be, but the suggestion I've heard that I like best is that he will have loved Harry's mother, though he probably hated Harry's father and dislikes Harry because Harry reminds Snape of Harry's father.