Do they get adopted by other instances? Are they still accessible from other instances? Can you still post on them from another instance?
Edit: From my understanding every instance that deals with a community has a cached copy. Will that copy disappear after a certain time, because it can’t phone to home anymore?
I think it needs the ability for multiple hosts to opt in to co-hosting a community. It could work as a cache and provide some redundancy if something goes down, temporarily or permanently.