I can understand why refederation needs to be done manually, but I'm confused as to why transferring users and histories is a maybe. Web and database hosting are mutually exclusive from domain hosting/registration.
With ActivityPub all of the primary ids contain the domain of the hosting server. So if you lose your domain none of the other instances know that you're the authority on those communities, posts, comments or users. So essentially federation breaks with all of the old data.
Same issue is why mastodon needs your origin server to be online to migrate to a new server. In both cases, federating a public key for the server or accounts would allow either to pop up at a new domain and prove it has the authority to migrate links to the new location.