What Would a Buddhist Do in This Situation?

In the zen tradition, we we recite the bodis at va, sentient beings, living beings, are numberless. I vow to save them all. So there is this this great responsibility there by traditional ways of understanding buddhism. If life on earth gets wiped out, and there's no humans left, then they'll have to be reborn somewhere else. What that means, where that somewhere else is, i don't know. But the idea is that the carmic tendencies that cause suffering would still require some kind of rebirth. And some buddhist would say, if why?