JKR has said in interviews that death is permanent and forever. She doesn't want to confuse the kiddos that their loved ones may come back.

He is dead but will come back in some form to help Harry. I also think that he and Snape were in on it together, that Snape really is a double agent, on the side of Dumbledore to help Harry. I think when Dumbledore was begging he wasn't begging for his life, but for Snape to kill him for the greater good.

JRK is the Queen of red herrings. Does anyone else think that Harry is the ultimate red herring? Or is that just sleep deprivation talking.

I’m doubting that Dumbledore is actually gone and that Snape is really evil. Rowling loves to put in little hints that you don’t realize until later, and this book seemed chock full of them. Most obvious of which, Dumbledore’s attempt to turn Draco around. From page 592. “I can help you Draco... He cannot kill you if you are already dead. Come over to the right side, Draco, and we can hide you more completely than you can possibly imagine... Nobody would be surprised that you had died in your attempt to kill me... Nor would the Death Eaters be surprised that we had captured and killed your mother...” He’s talking about faking one’s death! And later, “No Draco, it is my mercy, and not yours, that matters now.” Obviously Dumbledore is in control, and I also believe that his later pleading was simply to add to the ruse. Further, I do not believe that he would have stunned an invisible Harry, forcing him to watch the horror of Dumbledore’s murder, unless he had a great reason. And what better way to convince the world, and your enemies, that you are dead than to convince the ones who love you most and who are closest to you? If Harry believes, Voldemort surely will. And getting ultimate credibility for Snape from Voldy at the same time? Perfect. Further, in OotP Dumbledore remarked how much easier it was to accomplish tasks when released from the school. Well, now he certainly is released. But the thing that did it for me was this, from page 645, “Bright, white flames had erupted around Dumbledore’s body and the table upon which it lay... White smoke spiraled into the air and made strange shapes: Harry thought, for one heart-stopping moment, that he saw a Phoenix fly joyfully into the blue...” Rowling never adds a “so-and-so thought they saw such-and-such” unless they actually did. Remember Draco catching a fleeting glimpse of Harry’s shoe? And the fact that Dumbledore’s body disappears behind flames that diminish to reveal the tomb, with nobody seeing his body actually interred, seems like the old “smoke and mirrors” bit to me. And last, I sincerely doubt that Rowling would have made Phoenixes so central in the books if it weren’t for something like this. Phoenix means returning from the grave, at least metaphorically. I’ll be surprised if he doesn’t return.

My own suspicion is this. He is, through it all, good at heart. His malice towards Harry stems from his malice towards James, which in turn springs from, I believe, intense jealousy. I believe that Snape was (wait for it!!!) in love with Lilly, and he hated James, his tormenter and sworn enemy, for stealing her heart. Remember that when Harry was in the Pensieve, watching Sirius and James bully Snape, it was Lilly who intervened and made them stop (and, incidentally, we now know that she was a master potion maker, a major attraction to someone like Snape.) Snape’s harsh names thrown at her were just in reaction to being embarrassed. He loved her, and ultimately caused her death after hearing the prophecy. I believe that this is why Dumbledore trusts him completely. He knows that Snape’s heart broke when he realized that he had caused the death of the woman he loved, and therefore was forever committed to righting that wrong. Imagine; what if Harry was less pure and strong, was deeply in love with Ginny, but she fell in love with Draco, and Harry inadvertently got her killed. I imagine that he’d act much as Snape does. Also, if Snape was truly Dark enough to murder Albus Dumbledore, he wouldn't have simply knocked out Flitwick and left. If Snape was a true Death Eater, he would have killed him, knowing that he was an enemy of Voldemort. No, Snape is still undercover. Deep cover, now.

As for Dumbledore, I’m going to play Devil's Advocate a little here. I still believe the theories which I posted, but I can’t help but wonder if those same clues that I picked up on could actually be proof that Dumbledore isn’t coming back. Here’s why. These books are kids books. Yes, adults are equally in love with them too, but still, they’re kids books. And kids books share the common trait of teaching lessons. I wonder if, perhaps, Dumbledore’s death is such a lesson. In OotP, when Sirius died, the reader experienced it through Harry. We saw how Harry reacted; his disbelief, hope that it wasn’t real, gradual acceptance, coping with grief, etc. I wonder if that was “Death Lesson 1.” Now, with Dumbledore’s death, (Lesson 2) the reader experiences death for themselves. Where before we lamented for Harry and his pain, we now lament at our own sense of loss. And all of Rowling’s clever little clues, giving us hope that this isn’t real, may simply be a way of creating that feeling of disbelief in the reader, just as Harry felt it for Sirius. “No, he’s not dead! Look at this!”

So, I have to wonder if this is all Rowling’s way of teaching kids about death, and loss. With the funeral, the way her descriptions pulled you in so that you felt that you were there, experiencing it, feeling it; and now the long, slow path of acceptance, it definitely seems plausible. I hope that this isn’t true, but it wouldn’t surprise me if it is.