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?
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.