The Clojure/core team helped tremendously by many brilliant people volunteering fixes, features, and docs -- just like now.
However, I think the question was about projects built with Clojure, i.e. how to ensure that future developers in the company I work for will be able to continue where I left off? The global Clojure talent pool, while growing, is still on the small side (e.g. compared to even Ruby).
http://janestreet.com/minsky_weeks-jfp_18.pdf See part 4 "Personnel" for Jane Street's experience hiring OCaml devs.
That said, I don't think the matter is quite that straightforward where I come from; I would imagine Clojure dev head count in the whole of Finland is in the low double digits. If I were making business decisions involving future staffing, I would not feel confident I could replace the (hypothetical) only in-house Clojure dev in this job market.
That said, as others have noted, if you're hiring quality people, there's no reason they can't learn Clojure on the job. Plus if you make an investment in your people they're more likely to be invested in you ;)