Hello and welcome to the Flow forum! 
I would take it off ASAP, otherwise they will put propolis all over the Flow super, which is a BAD thing⌠
Bees often do not cap the last honey of the season. Couple of reasons for that. First, the weather is cooler and it is harder for them to work their wax flakes into caps. Second, they know that âwinter is comingâ and it is a waste of energy to cap something that they will soon need. If the brood box(es) is/are stuffed with honey, they will have nowhere to put it, you are correct. So you should take it and feed them something suitable for cooler conditions. Once the night temps drop below about 55°F, they are often reluctant to take syrup, as you probably know by your fifth year, so fondant or solid sugar would be good.
For my last harvest of the season, I harvest in my kitchen. That is because there are almost always large areas of uncapped honey, and I donât want a leak in the hive. I use a bee escape below the super to clear out the bees for 24-48 hours, then drain the frames using a setup like this:
I test the honey using a honey refractometer (about $30-40 from Amazon) and if it is 18.6% water or less, I am happy to sell it or give it away. If the water content is higher than that, then I freeze it, and the bees get it back later as a spring feed in a standard in-hive feeder in February or March - whenever the temperatures are back above 55°F.
Please ask if anything is not clear.