From a friend in England (perhaps old news but new to me):
JKR was on a BBC chat show on Friday and she said that while finishing the book, she killed off two characters who hadn't originally been slated to die. But she made it clear that they weren't the ONLY two characters who die: 'It's a bloodbath.' she said firmly 'well, not a bloodbath, but more than two die.'
So at least three. But please, not Luna.