I assume you are talking about the question about an asteroid impact that came up in one of the live chats.
I think the best thing would be to avoid an asteroid impact altogether. By tracking the asteroids you can make a guess about which ones might come near the Earth. If we have enough early warning (say at least 10 years, preferably longer) then maybe the trajectory of an asteroid could slowly be modified so it misses the Earth. There are a few ideas about this, like wrapping one side of the asteroid in foil, attaching an engine to it etc.
Hopefully we’ll get enough advance warning so that we can send a spacecraft (with Bruce Willis on it) to alter the course of the asteroid somehow, to avoid collision. Even if we cannot avoid it completely we could try to minimise the effects by directing it to, say, Siberia.
Unless the asteroid is absolute massive and smashes the Earth into pieces, I think the main consequences would be the direct hit, a tsunami if it hits an ocean, and a change in the Earth’s climate. At least in principle, the first two can be handled by evacuation, but the climate change caused by the impact is much more serious in the long term, so the main thing we would need to do is to understand how we can handle it.