I’m glad you decided to just get it done, for now. I’ve been in the same position, and getting something like this to work when you’re under time constraints just isn’t worth the headache.
I got to wondering - does the progress window have any sort of cancel button on it? Because if it does, and that button doesn’t appear anywhere else, then you can use a “Pause until” to wait until the button doesn’t exist.
One of the difficult things about what you’re trying to do is that the progress window probably doesn’t stay up long enough to test a bunch of different things. If you really want to get this to work, you should make a really long track, perhaps by copying and pasting a track onto the end of itself until it gets really long. This way you can thoroughly test the different methods of determining when it’s done.
Actually, I think it’s a great combination. Nothing like being able to start it and walk away. I’ve got several workflows in FCPX that I can’t imagine doing any other way. I’ve even got a search and replace for changing clip names that can search hundreds of clips without me needing to do anything except sit back and smile.
Anyway, best of luck.