I think that

...
[sblock]
Voldemort has already won, and won completely, as of the end of Book Six.
Harry Potter has said he would not return to Hogwarts if it reopened. Consider that, folks.
At the end of Book One, he practically considers it his home (in the film, he says this, but in the book it's pretty much implied.) Now ... he wouldn't return to it, if it reopened? He has gone from considering it home, to hating it to the point of never returning, even to finish his education?
Voldemort did this. Voldemort sent his people in to bring grief to Harry Potter. And Voldemort is indirectly responsible for the horrors visited on Harry by many other people. Most of Harry's bad Hogwart's experiences stem from Voldemort ... and they have added up and now Harry hates the school even more, it would appear, than he hates the Dursleys.
And now, consider this ...
Hogwart's is a heavily fortified fortress. If you take the combined strength of Voldemort's enemies and the student body (the majority of whom oppose Voldemort) and their parents (if sheltered at Hogwarts) and those fey creatures who stand with Hogwarts, you have a strong army in a strong citadel.
Which is desperately needed because Voldemort is back in his full might, and he has his army fully readied and on the offensive now. And Voldemort is stronger than any opposing wizard in the world, in a one on one match. Dumbledore, his only equal, is dead and gone.
Harry Potter is smart enough to know this. Indeed, he and his friends remark on it before McGonagall foolishly closes the school (but then, McGonagall was never very smart ... )
Panicked parents trying to defend their children, alone in their poorly defended and/or undefended and/or undefendable houses, is a real bad idea right now. As Harry and his friends noted.
The Ministry of Magic? They are total incompetents, and they lost to Voldemort long ago. They cannot protect anyone.
So why would Harry Potter abandon Hogwarts, when he knows Hogwarts is the best defense his peers (including the Weasleys, and Hermione, and his other friends) have?
Or does Harry simply not care enough about his peers anymore?
Perhaps Harry is so damaged from the way he has been treated, at Hogwarts (through Voldemort), at Hogwart's (due to the way things are done at Hogwarts), by the Ministry of Magic, and by others ... they he simply does not care anymore?
I think this is the case. The new Harry Potter: the Harry Potter who no longer cares, who no longer feels, who is hard and cynical and uncaring.
How could Voldemort *possibly* have won a greater victory, than to have accomplished this? I could not imagine a greater victory.
They could go and kill Voldemort completely (all those Horcruxes, everything) and all his followers ... but Voldemort has still won. He has won for all eternity, if Harry Potter has become the thing he appears to have become.
I must confess that this is extremely disheartening. But there it is. Voldemort has won. Voldemort is persevering, if nothing else ... and patience and perseverence pays off.
He has destroyed Harry Potter. Everything else he does, from this point forth, is chickenfeed in comparison.[/sblock]