What actually happens to the communities whose instances shut down?
Is it still possible to interact with the communities (post, vote, etc.)? If yes, is it still possible to delete them if the ownership of the community (aka the top mod) belongs to an user from another instance?
I believe you can reply locally on your instance to dead communities, but that data would never be replicated to other instances. The fediverse isn't really a mesh network, more like a hub and spoke on a per community level.
Yeah, pretty sure this is it.
If I understand it, the communities are stored on the instance and when other instances interact they call the home instance to create a localized copy updated with each interaction. When things are deleted, they're deleted first on the home instance and whenever the call goes through to update the interacting instance. If an entire instance goes under then updates from the home instance never get called, and no new interactions are hosted on the home instance, so it's as if the link between interacting instances is broken.
This could probably end up with a lot of fragmented instance interactions taking up space on connected instances after a while, but at least it isn't any worse than just regular increased activity.
Lemmy works on vampire rules. When an instance shuts down, its 100 most prominent users turn to dust and blow away IRL.
Looks like a support question /s
More seriously https://lemmy.world/c/moviesandtv@lemmy.film is a good example. Local users can still interact. Sometimes they don't even know the instance went down.
I would assume if the instance shuts down this means at the next point of sync the instance will disappear from your radar, pulling all posts and accounts and communities from that instance.
Iirc the likes from your account on that instance's posts might be either completely removed (because the post doesn't exist anymore) or they are in limbo but invisible and inaccessible, although I have no clue how that would work.