You can register on a Piefed instance and use Lemmy’s subscription export feature and Piefed’s import feature to retain your subscriptions. Porting comments/posts isn’t a thing.
There’s work underway creating migration scripts for Lemmy databases to be imported to Piefed, but that is a tool for instance administrators only, of course.
All the good luck with that!
These things happen, can’t expect five nines from every server.
—Sincerely, some girl who once ran a minimal resources server off of DSL and janky Debian hax