I think that depends.

Sometimes maintainers either burn out, lose interest, or have other projects take up the time that they used to spend on maintaining that particular package. Maybe they don't have the whatever it took to keep up with that maintenance, but they might be able to put in a one-time handover.

Or, sometimes a maintainer knows they're going to have to orphan a package ahead of time, and look for someone (or a group) to take over. If they get new maintainers up-to-speed before they have to drop it, a formal handover to "maybe follow the fork by user X" at the end of that could also be useful.

But not a requirement. And you'd probably want to make it opt-in on a per-package basis rather than switching users automatically. And users could always switch forks at any time, anyway, if another one turns out better.