Let's say you mean something like what Gordon describes here. https://subconscious.substack.com/p/credible-exit
It says it in there: DNS is a pretty good start. Regardless of social protocol, you can get some kind of credible exit by letting end-users bring their own identifier to the social service provider. Mastodon doesn't do that.
But it should be considered best practice to have your ActivityPub Actor ID use a different domain from your inbox provider. https://bengo.is/actor.json