The end is near... Harry Potter book seven hits stores in a week. I think we've figured out how it ends... so don't read on, if you don't like mere speculation or spoilers, even.
I've read the other books out loud to my children by candlelight, so yes, I think I am somewhat of an expert. We decorated an entire HP tree for the Festival of Trees, including my dad making a real working "Monster Book of Monsters" that bared its fangs and growled as people walked by! We are broken-glass-wearing, wand carrying, Rowling-quoting nerds around here... read on if you dare....
First, let us establish that JK Rowling will likely not kill off her beloved main character. Although she has long been quoted as wanting to "put the series to a complete and final end", she is very aware of keeping her fans happy - and killing Harry, well, that would not make anyone happy. He has become, in such a short time (in the literary world) a beloved character. If she kills him off, will anyone be satisfied? She wants an ending that will prevent sequels being written down the road by others, like what happened to Gone With the Wind. She simply doesn't want anyone feeding off the money-machine she created, or messing with her characters.
Also: this is the biggest build-up since the end of the Sherlock Holmes mysteries... she knows that a lacklustre or unsatisfying ending will haunt her like a dead girl in a bathroom (Moaning Myrtle) or an ex-husband in a shower (Bobby Ewing).
Snape: Friend or Foe? That is the question. He appears to be foe... but why ask, at the very end if he will be a friend? He's been such a foe... how could he ever be a friend?
The first novel: Harry survives the attack by Voldemort that killed his parents but left him with a scar that seared in pain if Voldemort came near in subsequent books. One of several horcruxes, the darkest of the dark arts, yes, that Voldemort planted in Harry's little head, of course he is unable to kill Harry, his forehead holds one of the very pieces of he-who-shall-not-be-named's soul, he has been miserably gathering them up in the last five books at least.
So here is how Buddy and I cracked out it's ending: Harry is the last of several horcruxes that Voldemort spread out before vanishing. He needs Harry's death to retain his horcrux, and thusly, his power. Harry realizes this and decides to kill himself. How obvious.
But wait! Professor Snape, now instructor of Defense Against the Dark Arts, emerges to explain - there is another way! But Harry must jump into the floo and leave by whence he came, returning to life as a muggle, leaving behind his friends, his magic life, the only place he ever felt like he belonged... and return to muggle world, knowing forever that he made the ultimate sacrifice to save Ron and Hermione (who are now hopelessly in love of course), Hogwarts and all of it... Harry says goodbye to Diagon Ally, never to return. His future in the muggle world unknown but certainly fraught with unhappiness, no family or friends, and at this point, no career training? How's that for the ultimate ending? No wonder Rowling cried when she wrote it.
PS. With Snape sending Harry back to muggle world, he gets to take the credit for banishing Voldemort, forever.