nobody outside of your instance will see anything you post there

So you are saying that if let’s say a user from lemmy.world makes a post to the post-shutdown lemm.ee community, only users within lemmy.world can see the content? Did I understand that correctly? Basically each instance has a "copy of lemm.ee’s community, and lemm.ee` is acting as the main distributor of events between these “isolated communities”.

Is there any indication for the lemmy.world people to notice that the instance hosting the community is gone? Wouldn’t there be cases where users continue posting to a community who’s instances have shutdown, without realizing that they are not visible outside?