If Unlimited Void were proven to permanently reduce Thragg to a brain-dead non-combatant, that would obviously count as a win for Gojo even if Gojo never physically destroys his body afterward. At that point, the fight is already over. Thragg’s body still existing would not matter because he would already be in an irreversible losing state.
The same logic applies in the other direction. Thragg does not need to get through Infinity to force a win condition. If he can use his own speed, strength, flight, space survivability, and ability to keep functioning without a normal battlefield to create a situation in which Gojo cannot survive long-term, then that is still a win condition. It is not a direct one, but it is still a decisive loss caused by Thragg’s own attributes.
And to be clear, this only counts because Thragg can survive the conditions he creates. If destroying Earth would kill him too, then it would not be a win condition. It would just be mutual destruction. What makes it a win condition is not the destruction by itself, but Thragg’s ability to outlive the battlefield he destroys while Gojo cannot.
It also does not matter whether Thragg can destroy Earth in one hit or has to do it over time. What matters is that Gojo has no reliable way to stop him from escalating to that level once direct combat is off the table. If Thragg can keep pushing toward planetary destruction and Gojo cannot meaningfully prevent it, then the speed of the destruction only changes how long the loss takes, not whether it counts as a valid win condition.