This is an issue addressed by the Mastodon Server Covenant: https://joinmastodon.org/covenant
The Covenant includes a commitment from server admins to give users at least 3 months of advance warning in case of shutting down
That's an agreement with no teeth, they can just shut it down without warning, and then what do you do.
If this is very important to you, then you should find a server admin that you trust, such as a friend or a fellow industry professional.
You can also use a paid instance like https://cloudisland.nz/ or set up your own using a hosted service like masto.host
Re:Twitter Suspends @Joinmastodon
by scrollaway on Thursday December 15, 2022 @08:16PM
(#34008239)
I agree with you. Mastodon does make it easier to migrate between users. ActivityPub (or is it Mastodon-specific?) has something built in to broadcast account migration announcements, supports account aliases, carry followers over, etc.
It's better than email in that regard.
Re:Twitter Suspends @Joinmastodon
by davidgerard on Friday December 16, 2022 @04:00PM
(#34020303)
Any techie on HN could run a one-person instance. Mastodon itself is fat, but Pleroma/Akkoma and Misskey are smaller, for instance. I know someone who's writing software for a one-person server in Rust that is intended to deploy as a single binary file.
The problem you describe is real, though, and it's the least friendly thing about Mastodon for new users.
I'd pick a large instance to start with, and move at your leisure.
I'm camped out on a friend's server right now, he said it was strictly for amusement but he's having a whale of a time being a Mastodon admin. When he says he'll definitely give us 2mo notice if he gets sick of it, I know I can trust him on that. That sort of thing.
I feel the response might be something akin to "what would happen if you have a fastmail account and then fastmail closes?". If that's the case, I see absolutely no reason to choose a small instance, just for the sake of reliability and trust in its continued operation.