This is my theory I have been thinkin about:
I think Dumbledore could be an animagus. I think he can transform into a phoenix. Think about it. Dumbledore's pet is a phoenix. His group to fight Voldemort is called The Order of the Phoenix.
Well, with all of that in mind, I think Dumbledore is NOT dead. However, for the sake of argument, that's just say that Snape did kill Dumbledore. Right after Snape kills Dumbledore, Faux flies over Dumbledore's body and cries. Remember that phoenix tears have healing powers. I think Faux's tears healed Dumbledore's body somewhat. Since Dumbledore is not a fully fledged phoenix, I don't think he can immediately die, flame up, and be reborn from his ashes. I think he needs some help in order to do all that. I think Faux's tears help Dumbledore's body to eventually flame up and be reborn. So at the funeral, when Dumbledore's body suddenly flames up, I think he is reborn from the ashes. I also think that he transforms himself into a phoenix, and flies away. Remember that Harry thought he saw a phoenix fly away from the smoke.
So technically, Snape did kill Dumbledore fulfilling his unbreakable vow. However, Dumbledore is NOT dead because he was reborn from his own ashes.
Well, what do you all think about my theory?