(Plausible) Harry can stall for time by explaining his discovery of Mendelian magical inheritance, and the implication that magic is not a property of Wizards but rather bestowed upon them, possibly by the Atlantean Matrix lords. This is a power, or at least knowledge, the Dark Lord knows not, and it gives him time to do his Partial Transfiguration attack, while also not giving Voldemort any kind of immediate strategic advantage.

(Implausible) This would then segue into a discussion of whether Voldemort is just seeing his CEV, and simulated-Harry trying to break it. Somehow, they end up breaking the Mirror's illusion, thus destroying this "world".