Theories about Harry Potter 7: what do you think (don't read if you haven't read book 6)?

I do believe Snape is good, and that the argument between he and Dumbledore wa sthat Snape didn't want to go through with killing Dumbledore. However, I do think Dumbledore is dead. Snape's unbreakable vow with Narcissa required that Dumbledore die. If Draco failed to kill him, the Snape had to do the job. That means that if Dumbledore didn't die, Snape would have broken his vow and died himself. Besides, JKR has stated publicly that Dumbledore is dead and won't be returning. I know she likes red herrings, but if he returns, then she would have told a baldfaced llie.