Still, the very definition of risk mitigation is there is a chapter entitled "What you can do when the unimaginably awful happens." For example, in the USG we have continuity of operations plans and the last chapter is literally "Catastrophe Mitigation," where the event is left undefined but it stands for "even worse" than the specified scenarios. Considering one of the specified scenarios is nuclear war... Anyway, the Catastrophe Mitigation is a set of protocols that depend on what's left: do you have infrastructure, do you have comms, do you have a command structure, etc. At each stage there are steps you take to try to prevent even more massive damage. This is actually one of the key responsibilities of government.
