As far as I know, there isn't an account migration mechanism in Lemmy yet. I've heard (fourth hand at best) that it is in the works but hasn't been implemented yet. You may have to do it the hard way. Copy, paste and search.

I would just wait before doing any crazy. I would assume they can get a new domain, and migrate current environment there. Probably causes few issues for few days.

If you want to support smaller instances (which is of course good), then you should create new account somewhere.