I always knew that Dumbledore would die. He had to. If Harry and Dumbledore face Voldemort together, where's the tension? Voldemort and Dumbledore one-on-one would be difficult enough for Voldemort. (I'm leaving out all of the supporters on each side...)
The other reason is that if Dumbledore comes back, she needs to be extremely creative as to why. Gandalf came back, and Dumbledore began as a quasi-Gandalf character, and I think Rowlings is aware of this.
I believe, without hesitation, that Snape is good. Here's why, including Dumbledore's reactions, because they are significant.
1.Dumbledore was pleading (Severus, please) – but he didn’t plead for his life. I think that is significant.
2. Dumbledore, without a wand, and surrounded by many that wanted to kill him, was the same old Dumbledore – reacting to their snide comments with his usual humorous and dismissive tone, just as if he had his wand and was quite capable of using it.
3. While he was surrounded by these horrors, he showed no sign of fear whatsoever. Absolutely none. He simply talked. (I think he was talking to give Snape a chance to reach them to take the onus off of Malfoy. See below).
4. When Snape – Professor Snape <grin> - appeared, Dumbledore's mood changed entirely, and he said
Severus…please…
Can *anyone* imagine Dumbledore pleading for his life? I can’t. When I read that sentence, it was the only time I’d ever seen any of Rowling’s characters step out of character – seemingly.
5. A far more logical plea is that he didn't want Malfoy to be the one to kill him. Once you kill, you can never take it back. You've gone to "the dark side". Dumbledore obviously would want Malfoy to remain an “innocent”, even though he is aligned, by blood, with darkness.
6. Rowling writes,
Snape gazed for a moment at Dumbledore, and there was revulsion and hatred etched in the harsh lines of his face.
That could easily be explained away as Snape’s fury that he has to kill the man who trusted him, and stood by him unwavering against everyone – teachers included – allowing him a new life. Dumbledore refused to ever hear a bad word about Snape.
I believe that Voldemort could be tricked because of his lust for power. I have a difficult time believing someone, even with Snape’s power with Occlumency, could hide something from Dumbledore. Dumbledore isn't confused by the same lust that drives Voldemort. His mind is clear.
7. Snape is not a quiet man; he tends to be boastful, or, to Harry, quite mean.
Yet when he kills Dumbledore, he doesn’t speak a single word. Not a word. That may be the single most important piece of “evidence”. If Snape really hated Dumbledore, I can’t imagine that he wouldn’t have a few words to say to him, such as, “You were a fool to trust me…” Frankly, I would expect a litany of hatred spewing from him prior to killing Dumbedore. Or, given the time constraints they were under, at least something of significance so that the others (Draco and the other Death Eaters) would be convinced of his loyalty to Voldemort. I see his lack of speech as entirely out of character. The second time, only the second time, that Rowling had one of her characters “step out”.
8. When Harry was chasing after Snape, Snape
could easily have frozen him (I forget the name of the spell that renders a person incapable of movement). Instead, Snape allowed Harry to chase him, allowed Harry to try and throw spells at him. Yes, Snape did have a few comments for Harry’s filthy, cowardly father, but he also said this, which I believe overrides his hatred of Harry’s father:
Blocked again and again and again until you learn to keep your mouth shut and your mind closed, Potter!
I really believe that statement was intended to remind Harry that the most powerful wizard is one who can block his thoughts (and I think Snape used his Occlumency [sp?] to hide his thoughts from Voldemort or others of the Death Eaters), and cast spells without speaking. As I said above, I think that Voldemort would be far easier to trick than Dumbledore.
9. Harry called Snape a coward several times, and Snape finally completely lost it. Why would that word have such enormous significance to Snape? Nobody that was a coward would be pretending to be on Voldemort’s side but really be on Dumbledore’s side. Snape was risking far more than his life if indeed he was on Dumbledore’s side – and if that was the case the very last thing in the world he could tolerate is being called a coward. If I was in his shoes, I think I might finally go off my nut as well.
10. That exact quote is:
DON’T – “ screamed Snape, and his face was suddenly demented, inhuman, as if he was in as much pain as the yelping, howling dog stuck in the burning house behind them – “CALL ME A COWARD!
Rowling has always said that everything we need to know is in the text. I think this is where it is.
Why would Snape be in pain?
Okay, I've bored everyone enough. This may not work for some, but it convinces me.