Some obvious theorycrafting: (presuming, based on Hermione's resurrection, that Voldemort's plan is for Harry to rule the world): (note: Quirrel did mention once before in Parseltongue: plan iss for you to rule country, obvioussly.)

• possibility 1 (The simple and obvious version where Voldemort finally makes a mistake): Original plan - Voldemort plays the role of antagonist or whatever while Harry rules the world openly. However, the horcrux network glitches when Voldie tries to plug Hermione in, and we get what we see (Voldie supposedly dead, Harry wins).
• possibility 2: (Voldemort actually won) Unless Hermione can in some way detect the Horcrux network, there is no easy way to test whether Voldemort is really dead or not now. As Quirrell himself mentioned at some point, what worked once can work again, given the sufficient stupidity of audience, and it definitely seems now that Hary has once more vanquished the Dark Lord. The result is: Dumbledore is gone, Voldemort is free to assume any new identity he wants to and continue the game without anyone knowing about it, Harry is a hero and Harry gets all the toys and a resurrected Super-Hermione, who otherwise would have probably never agreed to undergo such rituals as human and magic creature sacrifice for the sake of her longevity.

For the second possibility - If there was anyone Voldemort could have been altruistic to, it's himself, and Harry is sort of, well, him. I could theoretically see how Voldemort in his twisted ways would consider his gambit a great gift to Harry - Harry has Hermione back (and better than original), Harry won't need to bother about Dumbledore while working towards his world domina... i mean, optimization, of course!, and Harry gets a load of cool toys to play with. So if we suppose that Voldemort is capable of limited empathy towards Harry - maybe he did decide to have a Grinch-Heart-Growing-A-Few-Sizes moment and give Harry such a nice, bloody and traumatizing gift? I feel that is more probable than the great Chessmaster Riddle finally making a mistake... though, as someone already mentioned, Dumbledore could have somehow loaded Voldie up with a nice overdose of Bahl's Stupefaction.

p.s. On the second thought, an additional correction. Provided that it was really Dumbledore that killed Draco's Mom, now that Dumbledore is conveniently gone by Voldemort's hand, Harry doesn't need to choose between his friendship with Malfoy and his wise old advisor. This assures me even further that what we observe is an unprecedented act of twisted altruism from Voldemort to his Mini-me.