Maybe a handful of them. One of them was an extremely prolific (#3 contributor to Nixpkgs) and active contributor that no doubt everyone will miss. There's at least one other name I recognize on the list. But most of them are pretty small-time maintainers so far.
> I also don't really get it; are they going to use a different (worse) OS because of this?
They're saying they're going to fork. There's one fork emerging already, but idk if it'll be the one. I hope a productive and usable fork does arise (and that eventually it can rejoin Nix) but I'm pessimistic that any will survive.