Harry survives, Voldemort is destroyed, a "comedy relief character" finishes the series as a tragic hero, and Rowling can't be accused of coming up with a cheap trick to resolve the story.
Good theory, but I'll wage dollars to donuts that she kills both Voldemort AND Harry off. Harry will probably die sacrificing himself for everyone else but will manage to kill Voldemort in the process. Although given the twists and turns in the previous 6 books, I can see her toying with the idea of having the bumbling Neville Longbottom, turn out to be a hero. I think the main reason why she'll have Harry killed off, is so that, in her words, there can't be any sequels. It's kind of silly though as she has copyright on the books for what-----60 or 100 years? That's why there wasn't a sequel to Gone With the Wind for 60 years----Margaret Mitchell died not too many years after the movie came out, and they had to wait for the copyright to expire.
I can see a couple of things happening: At the end of book 6, Snape kills Dumbledore. I can see her having that whole thing as a set-up and perhaps Dumbledore isn't really dead----it was done to throw Voldemort off. Or, if it wasn't a set up, I hope she has Neville kill Snape as the poor kid was terrified of him throughout.
And then, they could have a couple of Jehovah's Witnesses coming knocking at the doors of Hogwarts School of Witchcraft and Wizardry, and start bible studies and convert the whole lot of them. Voldemort becomes President of the WTB&TS, along with Professor Snape and Lucius Malfoy.
