It seems that once the evaluation is done, there will be a indication in the mini-buffer. Just trust, and be patient.

Return value gets shown like this?

Also, in the latest doom version, you should see a loader in your CIDER repl's modeline e.g.

(require '[clojure.core.async :as async])
(do (async/<!! (async/timeout 5000))
    (println "done"))

sounds like a Turing-undecidable problem to me :) in practice you can wrap a slow sexpr in println so that it goes to your repl eventually, which seems a little more durable than the UI widget. You also can inspect thread dumps (`Ctrl+\` , yourkit etc) and see if there's a thread named nrepl-worker-foo that is currently doing something related to your sexpr.