“End of current civilization” is much more likely, but that can be accomplished without asteroid bombardment–our nuclear weapons arsenal is capable of it, and it will end when the fossil fuels run out in any case. Industrial agriculture can’t be maintained without the petrochemical-derived fertilizers, pesticides, and herbicides we lavish our crops, and poison our waters, with. And without industrial ag, there’s no way to maintain our current population.

There’s a difference between “might” and “will.” Our fossil civilization has a couple of centuries left at most; a civilization-ending asteroid isn’t likely in such a short time-frame. And flight to some other planet isn’t likely to save us from civilization collapse, as there are no other ecosystems “out there” to flee to, and we have no idea how to create, from scratch, a functioning, stable ecosystem. All of our attempts to date have failed.

I’d prefer policymakers focusing their efforts on that which will happen before addressing that which might happen.