External dependencies you manage like in most other applications nowadays, you don't hit external services in the "guts" of your code unless you really need to, for performance, testability and to keep the less reliable parts of your code isolated, you keep the interactions with external services as close to the "main" of the application as you can.
When things break down is with more complex data models of the application, not even as much because of the language itself but because Clojure programmers actively reject using record types and interfaces, and just pass dictionaries around. You wind up with some code that, bafflingly, gives the impression of being very simple and neat, but you can't tell what it's actually doing.