I wouldn't predict his death at this point, but I do think people should pay close attention to Neville Longbottom. J.K. Rowling has said that Neville's story is important for the overall plot. Indeed, she has gone as far as to have him born on the same day as Harry Potter, the other figure to whom Professor Trelawney's prophecy might have referred. Something is going to happen with that kid, perhaps the best candidate for a Tolkeinesque ennobling of the humble.
Another point raised by Guinn is the betrayal of the hero. This works for King Arthur, but in Tolkein all the betrayals were early and didn't involve anyone to whom we got emotionally attached, so I don't give it the same importance he does. It is, however, an interesting idea. Any speculation on potential traitors in the current cast of good guys?
Finally, while I managed to sort of invert the plot, several of the notions I had before Order of the Phoenix remain as unresolved issues.