Yes indeed, giving proper notice seems like minimal etiquette. Then again, life happens. Admin may be caught in some tragedy making maintaining their lemmy instance not exactly a priority, or they may even be dead.

There is not much you can do to just migrate your account somewhere else, that's a limitation of federation (compared to fully decentralized protocols, like Secure Scuttlebutt), but I'd wish Lemmy would implement ActivityPub's following endpoint, so we can easily build scripts to backup the communities we're in.