At some point Insurance is going to require companies to obtain paper copies of any documentation/policies, precisely to avoid this kind of situation. It may take a while to get there though. It'll probably take a couple of big insurance losses before that happens.
Digital copies will also work I don’t understand why they just don’t save both the URL and the content at the URL when last checked.
More likely, there will be trustee services taking care of document preservation, themselves insured in case of data loss.
Also, getting insurance to pay for cybercrimes is hard and sometimes doesn't justify their costs.
We already require all relevant and referenced documents to be uploaded in a contract lifecycle management system.
Yes we have hundreds of identical Microsoft and Aws policies, but it's the only way. Checksum the full zip and sign it as part of the contract, that's literally how we do it