Actually, I've seen that same exact theory. I think it's been apparent for a while that one of the three besides Harry is going to die (I mean, look at the characters in relation to Harry that have been killed: parents, friend (Cedric), father figure (Sirius/Dumbledore), and mentor (Dumbledore)). The only thing that's missing is a close friend or love interest, but I don't necessarily see Ginny or Cho being too involved in this because Harry isn't going to want anyone to get hurt (the Spider-Man never wants the Mary Jane to get involved). Frankly, it's the manner in which they die that is going to be the most significant, although a sacrifice seems to be the most meaningful/logical at this stage in the game. I say this because, frankly, Harry hasn't had the most dueling experience. Sure, he's survived what he's been through, but he's not all that good offensively speaking and his heart never seems to be in some of the particularly nastier curses there are (I'm assuming an Unforgivable Curse is forgivable if you kill Voldy with it?), so that complicates the final battle, unless he runs Voldy through with like....Gryffindor's sword or something, which wouldn't surprise me.
The theory that is referenced by Cmash is in fact the spoiler from the "hacker" that I read. It's not overly surprising and the details aren't there, so knowing that won't surprise me too badly