You can indirect webfingers, so @you@site-you-own points to @you@someone-else-owns-this-server.
It's not ideal because there isn't a reverse link; if someone-else-owns-this-server dies, people who were following you on it will see you evaporate. But you can edit @you@site-you-own to point to @you@your-new-site so that at least people holding your ur-name can find you.
But unfortunately, there are few better solutions when someone else owns the data. One nice thing about the Fediverse is you can ameliorate most of this by setting up your own server (though I won't pretend that's going to be the solution that replaces everyone using Twitter; I maintain my own server and it is the same pain in the ass that self-hosting has always been).
The better solution is for implementations like Mastodon and Lemmy to let users bring their own custom domains, and have robust data export APIs. Then even if your home instance disappears overnight you can migrate to a different instance.
It's not ideal because there isn't a reverse link; if someone-else-owns-this-server dies, people who were following you on it will see you evaporate. But you can edit @you@site-you-own to point to @you@your-new-site so that at least people holding your ur-name can find you.
But unfortunately, there are few better solutions when someone else owns the data. One nice thing about the Fediverse is you can ameliorate most of this by setting up your own server (though I won't pretend that's going to be the solution that replaces everyone using Twitter; I maintain my own server and it is the same pain in the ass that self-hosting has always been).