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?
Afaik posts and comments are copied locally to federated instances so if the original went down you could still access what was once there from some other instance.
E.g everything (excluding uploaded images/videos) on https://sopuli.xyz/c/technology@beehaw.org would still be there without beehaw.
Once a user on instance A subscribes to a community on instance B, then instance A starts caching posts from the community on B. But to my understanding it doesn’t retroactively fetch all historical posts and comments.