Hmm.. Actually, thinking about it, I think that the most likely outcome is that Hermonie will be rescued by someone other than HP. Rereading the last chapter, Harry made absolutely no headway on the case himself, but he does succeed in something else: Persuading a great number of other people that this senario screams “setup” to high heaven—the very first thing he does : Explain Hermonines predicament to Hermonine. - this presumably sets her quite considerable intellect in motion on the case. Second thing he does: Alert the most formidable teachers, including Snape and Dumbledore. Note that my current theory is that Snape considers himself her mysterious old wizard, and if he intends to put in motion a gambit to get her off, this explains why he burned the notes. He is cleaning up any evidence that documents that he is her ally so that whatever he pulls, people will not look in his direction.
Then Harry successfully poked bits of the student body out of herd thinking by the offensive use of sarcasm. And those students have parents and relatives, some of which are on the wizengamot.
Honestly, after that days work, the wizengamot meet is nigh-certain to turn into a gambit pileup.
That is the logical conclusion your sympathies incline you to. I suspect that what Snape sees in HP is at best a future Dumbledore, and quite possibly simply voldy V 2.0 Why the heck sign up for being manipulated and a pawn a third time? Uh-uh. But this may entirely explain what the heck he was/is doing with SPHEW. He picked Hermonie as the potential future ally least likely to stab him in the back when convenient, and SPHEW as the bet least dependant on a single individual. (Because it is an idea. The idea that everyone can stand up and do the right thing.)
Without telling anyone. Which is hilarious.