@p_the_wanderer

The instances listed on https://joinmastodon.org/servers and https://fedi.garden have promised to give three months notice if they ever decide to shut down (plus also daily backups, at least two admins and responsible moderation).

I've also got a list of good instances by year of foundation at https://fedi.garden/servers-sorted-by-founding-year

Nothing's ever guaranteed, but these are perhaps good starting points?