I don't know that I could really see Snape giving his life to save Harry's, especially after seeing the way Harry's dad treated him. I'd think him more likely to give his life saving Dumbledore's, but yes, I do agree that Snape will not survive. I think I remember Rowling mentioning in one of the books that people who betray Voldemort won't survive his wrath, and Snape's turning spy is probably the ultimate betrayal.
I also doubt that Harry would be willing to fight for the Dursleys, though I guess I could see that happening, since Harry has a thing for saving people.
It does seem highly possible for Professor Lupin to become headmaster- that is,
if he survives, but I don't think the installation would take place so soon. Prejudices take a long time to get over, and human beings generally aren't partiularly fond of change.
The others, however, seem highly possible. Now I can't wait for the next books to come out!!
