Yeah, no. You can't simply disable Plesk like that.
I made the mistake of ordering a Plesk-based Linux virtual server thinking it was simply an additional- and optional- way of administering it.
But it soon became clear that Plesk was pretty much "baked in" to the setup and that I shouldn't be going "behind its back" and modifying files the regular way.
Similarly, I assume that anything I'd set up via Plesk would break if it was disabled, and I realised why their tech support had told me it couldn't simply be disabled later without moving to a new server.
Fortunately I realised my error quickly and was able to move to a new Plesk-less server before I'd wasted much time.
That's not to say Plesk is bad- it struck me as oriented towards managing larger, more complicated setups than ours. But it's definitely an "either or" and anyone invested in a Plesk-based setup isn't be able to simply move away.