They'd still at least buy reinsurance etc anyway.

All unlimited liability insurance companies (e.g. motor insurers in the UK) have reinsurance to take the hit on claims over a certain level - e.g. 100k, 1m etc.

For extreme black swan risks, this is how you prevent the insurance company just going bankrupt.

Reinsurers themselves then also have their own reinsurance, and so on. The interesting thing is that you then have to keep track of the chain of reinsurers to make sure they don't turn out to be insuring themselves in a big loop. A "retrocession spiral" could take out many of the companies involved at the same time, e.g. the LMX spiral.