If an event happened that caused the Earth's atmosphere to not be breatheable in a number of hours, would anyone survive? We may have the technology but do ther

If an event happened that caused the Earth's atmosphere to not be breatheable in a number of hours, would anyone survive? We may have the technology but do there already exist any artificial independent self-sustaining human habitats on Earth that would survive? We could try to build such habitats now -- it would probably be cheaper than going to Mars -- but I think we would have trouble forcing ourselves to spend the money and effort on it and have trouble keeping it honest (avoiding any cheats where it's mostly independent but still dependent on the Earth's ecosystem for some specific uses) without a separate goal (being on another planet) and a hard forcing factor (an environment that doesn't allow any cheats).