The bottom line is, they started something that’s bigger than them, and created more than enough tools to fork from them if they become a problem.
I always like to point to Emby/Jellyfin as a perfect example of how this is supposed to work. They created something excellent, the community joined in, and it got popular. Then the maintainers decided to try and cash in, and the community immediately responded by forking into what would become Jellyfin. And nowadays, the discussion is between Plex vs Jellyfin, you rarely ever hear people talk about Emby anymore.
After a certain point of user adoption, FOSS (and copy-left) software should be able to stand on it’s own without the creator’s direct involvement. The community can take the wheel if necessary. The Lemmy devs have provided enough tools to do exactly that, and I believe there are more than enough experienced devs in this community that we would not struggle to find the necessary talent.
That’s doesn’t mean there isn’t still a risk, though. This is social media, the technology is only half the story. The other half is getting people to move. I don’t think I need to explain to anyone here how hard it is to get an entrenched user base to abandon a platform whose mainteners have gone off the rails.