Thanks for the replies. So I guess USENET had/has an advantage here, as all USENET servers replicate “all” newsgroups automatically. To the extent that one server exists, the newsgroup lives on regardless of its origination point. In that sense, the collective work of all contributors is not lost until the retention date passes.
The ActivityPub proposal mentioned by @chris seems to be a good enough equivalent, at least for communities that are shared.