I cannot advise you on what to do about taking the box down, maybe someone else with more experience than I have will chime in here. I would think by now if Papa did not find another mate, he probably won’t yet this season. What is a slot box, I have never heard of them as far as I know. My 6 babies are still here so I am hoping they stay for the winter, but that is probably a stretch on my part thinking they might do that. Mama is incubating 4 eggs as I write this, they should hatch this coming Thurs. so that makes 10 this year if these 4 make it. Maybe a slot box is a good thing for me to look into.
I believe that it is late enough in the season to take the box down and replace it with the roosting. If they haven started to build a new nest by now, they are probably done for the year. Mine keep coming back to the box but have not entered nor put any nesting materials in the box.I have cleaned the box and am leaving it opwn to air and dry until mid fall when I close it for a winter roost.