Exactly my point: Zig managed to pass from a one-man-show stage to a more mature, more established stage. Same happened much earlier with PHP and Perl.
Elm, sadly, never achieved that. But I don't see why Borgo would necessarily follow the way of Elm and not of Zig or PHP.
If Andrew Kelly were kidnapped by aliens tomorrow, Zig would continue. I think that's the dividing point, when the bus factor is no longer one.