In such a case, it would be better if this were implemented through a separate additional option "Keep channels open when part", so that users have a choice.
And this should be disabled by default, so as not to call users nervous irritation ... [Linked Image from]

An example of how this might look:

    [Linked Image from]

Also it might be nice if it can be done via a command with a switch so that mIRC knows for sure that the user initiated it himself.

But this shouldn't work if the user wants to close the open channel window via the right-click popup menu.

I'm not sure if it would be a good idea to create something special for a separate service, in which parameters may change over time or another BNC service may be used.

I use "ZNC v1.8.1". Here is my log received in the "/debug @debug" window:
-> JOIN #testing
<- @time=2021-12-24T12:13:37.556Z :Epic!epicnet@ JOIN :#testing
-> WHO #testing
<- @time=2021-12-24T12:13:37.557Z 315 Epic #testing :End of /WHO list.
-> PART #testing
<- @time=2021-12-24T12:13:48.146Z :Epic!epicnet@ PART #testing :part

Commands used: "/JOIN #testing" ➔ "/WHO #testing" ➔ "/PART #testing".

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