the sole dev of both of these apps doesn’t think he needs any help and refuses to open source them.
Oof, that sucks. Seems like someone else needs to create an open source alternative app. The platforms themselves are libre software, right? I couldn't find a lot for loops on that, but Pixelfed itself seems to be.
All things considered, it's not yet falling off as quickly as I would have expected, maybe my memory is playing tricks on me, but I seem to remember Lemmy had a harder crash after the first reddit exodus, as did mastodon several times, when people fled xitter.