Hrung is correct, there are no commands to force a window to close. It is this lack of force-closeness which inspired my post on the matter. (and no, JOIN 0 is a server command, and will not work when disconnected)
If Khaled can make /window -c work on #channels too, and this would make people happy, then great!
I suggested a delay to try and prevent out-of-order (race conditions) from occuring, such as deoping someone and parting right away... mIRC would receive the On DEOP event for a closed channel. I'm not sure many scripts would be able to cope with that.