I wonder if the activitypub protocol (or, if not the protocol then some other layer) allows for the idea of "community mirrors". The way that the protocol works at the moment, as I understand it, only the host instance has a complete record of a community's posts and comments. But if there was a way for a community to designate one or more other instances as "mirrors" which maintain a complete sync of a community's content (going back all the way to the community's founding), that would lower the exposure to instances going down.
There would need to be a process (both technical and administrative) for a mirror to be designated as the new host instance should the original host disappear.
This would build in additional resilience into the fediverse model, by taking advantage of its distributed nature.