So in order to survive the colonies would need to be entirely self sustaining, and would only save humanity from an event that wiped out earth but left the colo

So in order to survive the colonies would need to be entirely self sustaining, and would only save humanity from an event that wiped out earth but left the colonies unharmed. Given the huge efforts that would be needed to create such colonies I think the work on spotting potentially dangerous asteroids and working out how to affect their orbits is probably a much better option.