Ron or Hermione -
They are very important characters, and JK has already killed an important character, who's to say she won't do it again?
Hagrid :
He is a semi-important character whom would be missed, but might not be of huge plot importance.
Snape :
Though I don't want this one to die, it is possible. Voldemort earlier stated that one who had left him forever would be killed. Snape was once a Death Eater and has supposedly left him.
Neville :
Not the most important character, but still one who has been around a while, perhaps he's expendable.