Unfortunately, at the moment it's impossible to rename/move your account to a different domain, and if your mastodon instance is shut down(which, let's face it,

Unfortunately, at the moment it's impossible to rename/move your account to a different domain, and if your mastodon instance is shut down(which, let's face it, is likelier to happen than twitter shutdown), you still lose your followers. You can host your own instance, of course, but that requires time/money for maintenance, and not everyone will do this.