There’s no committee, but there’s a sort of community-ish. Clojure is mostly maintained by Cognitect (a small company), and some of their employees are the active maintainers of Clojure, including Rich Hickey. They do seem to have some internal process for language change and proposal that they review and discuss within themselves, but it’s not exposed publicly.
Recently they were acquired by Nubank (valued at 10B), a Brazilian unicorn in the FinTech sector of apparently 2500 employees which uses Clojure(Script) almost exclusively (from what I read). They said they’d continue to invest in the growth and development of Clojure, and that seems to have been the reason for them acquiring Cognitect.
You can read the post about it here: Cognitect Joins Nubank
On top of that, there are a few external contributors as well who submit patches and the like.
ClojureScript is maintained by the community mostly, with David Nolen at its helm. If I got my history right, he used to work at Cognitect, but doesn’t anymore, but still maintains ClojureScript where Rich Hickey is no longer involved.
I’d say Alex Miller is the public face of the Clojure core team, and he also looks absolutely capable of taking over the helm in an unlikely event.
So my guess is someone else at Cognitect would probably take over, and if that folded as well, I could easily see someone from the community taking over.
Clojure is also less effort to maintain than most other languages, because it delegates a lot to the JVM, so a lot of the hard work of actually keeping up to date with various operating systems and hardware systems is handled by the JVM, leaving Clojure to focus on the higher level stuff. Also Lisps in general tend to be “easier” to implement. That is a good thing, cause it mean it wouldn’t take a full team of full time devs to take over the development of Clojure, but only one or two dedicated smart developers.
That’s hard to say. Every year there’s a state of Clojure survey. You can see 2020’s here: Clojure - State of Clojure 2020 Results
Based on the survey, Clojure’s use at work has been growing YoY, though at a slow but constant pace. Hobby usage seem to have plateaued, and thinkering is what’s down the most. What we don’t know is if the categories just traded with each other, people going from thinkering to hobby and hobby to work.
My impression is that Clojure has a small base of users, but that base is pretty healthy, but it’s not growing much. Unless people like you join off course 
What I mean by that base being healthy, is that I don’t think Clojure user base is growing very much, but the eco-system is definitely growing and healthy and hasn’t stagnated at all in my opinion.
Part of the reason why is that most things have a kind of 1% rule, where 1% of the users contribute like 99% of the bulk of the interesting and unique features. Even in a bigger community, with say 100 times more users, you’d still only have a handful making interesting contributions. At least that handful.in Clojure seem quite active and healthy.
@borkdude is part of that actually, the man is a machine of open source haha, he brought us clj-kondo, sci and babashka all in the last year or two. Those are immeasurable contributions. And there’s too many to list, but the eco-system is doing well. Editor support is at an all time high. Build tooling has never been this good. The slack is still just as active as before. There were some pretty great Advent of Code youtube videos, I recommend checking out by the way: https://youtube.com/playlist?list=PLbPrugU2oQ8VURsQdZ6W_iovXRS24UmZQ
I could go in listing more examples, like the MAGIC compiler to use Clojure for Unity game development, and others. Just to say, the ecosystem from what I see is quite alive and doing well, even if the user base may have not increased too much.
Edit: Oh and let me add that Clojure has a pretty healthy paid-for open source work as well. Clojurists Together (https://www.clojuriststogether.org/) funds 3 open source projects at 9k a quarter every quarter. And a few of the Clojure contributors have good patreon and github sponsoring. Cognitect even personally sponsors some of them: Sponsoring Open Source Developers Which I was told they spend in the 6-digits a year on sponsorship.