There are no dumb theories on this thread! We've been throwing all kinds of stuff out, just to see what sticks.
Maybe I should fix that: Ms. Rowling was going to call her sixth book "HP and the Pillar of Storgé, but when one of her publicist's former employees leaked the title, she had to come up with a new name." Think that qualifies as a dumb theory?
I do think Ms. Rowling has probably managed to create a cliffhanger on the level of 'Who shot Mr. Burns'; most of the lingering questions aren't as overt, but there remain far more nagging issues now than at the ends of the previous books. Since Ms. Rowling has said that the seven books will each cover one year of Harry Potter's education at Hogwarts, that would imply that the school will be open next year and Harry Potter will go back. The future of Severus Snape, however, remains an open question. My personal theory is that Albus left a memory for Harry with Ms. McGonagall, to be given to him only when there is no danger that Voldemort might discover Snape's true intentions. I would expect that if Ms. McGonagall were to give Harry a memory from Dumbledore in which he and Snape discussed what had to happen, that could allow Harry to trust Snape at a critical time. I don't think any of Snape's memories would suffice (since Harry would think they were faked) but Harry would probably trust Dumbledore's, if they were supplied by someone else trustworthy (like Ms. McGonagall).