I imagine users go poof. Are their profiles stored in other federated instances? Is there a way to recover them or “import from backup” onto another instance?
If they don’t have an e-mail I imagine you can’t even notify them or authenticate them elsewhere so this “import from backup” even if technically feasible (idk if it is) would be impossible in practice due to authentication issues.
And communities, can you even notify all your subscribers to move to the “backup community” on another instance? I saw yesterday that a Mastodon server host said “I’m deleting this instance in 2 days” or something like that and I started wondering how shit would go on Lemmy.
I can’t speak about kbin & Lemmy, however for Mastodon and Calckey there is a feature to export your user data and posts. You can then retain these for reference. Currently there is no ability to import them to a new instance – the technical reason for this is beyond me, but I believe it’s related to the UID of the posts as it is shared across the Fediverse.
People are working on solutions, and I have tested one which works well for Mastodon.
It’s very important to have the ability to extract your own data and move
Best would be if there is an app, that would do backups of your posts and content automatically, that if, for whatever reason, the instance goes down. You have first all of your data saved and second you could import it fast onto another instance.