I'm pretty sure if your honest all you projects end up having this bus factor (check all your dependencies). If you really care to look, most projects are run by a small group of people.
Interesting, why are compilers special in your POV? Why do they need regular maintenance and why don't they allow extension via some kind interfaces, thus allowing for less maintenance?
Elm is not something that needs regular security updates or something. It is super stable and has a relatively slow release cycle.
Even if the creator died or lost interest you would be still fine to use it. The community could still provide critical patches if their was a need. Feature development might slow down but if it is already offering everything you need that is not really an issue, no?
To add a little: the core features of the language are pretty well baked in at this point. Evan even said "If you like what you see now, that’s pretty much what Elm is going to be for a while."[0] The `eq` typeclass is I guess the missing feature[1] that stands out the most right now—in brief: don't allow equality check on functions, regexes, or JS objects at compile time.