Do an exploratory dig, not damaging the foliage and vines if you can help it. Harvest ones that are big enough to take. Try to assess if there are lots of smaller tubers or good % of tubers that are ready.
If it seems like they could use some more growing time, and long range forecast indicates temps going back up for a while longer, cover the vines with double floating covers or old sheets, etc. (or layer of permeable fabric and a layer on top of plastic). Be sure to remove the covers if during the day depending on weather conditions.
It's when the soil temp gets down in the... 50's? that you can lose the tubers to rot. That won't happen for a while as long as the daytime temp stays warm. You just need to protect the foliage from deep chill/frost.
If it doesn't frost but the temps are going to stay cool, I would try to extend the sweet potato season with a plastic covered hoop tunnel so they can get good and hot during the day.
Some weather stations are forecasting low of 38Ã‚Âº (not all however
) tonight or tomorrow night. I'll probably need to go through the same process.
...AND decide what to do with the tropicals in containers that have been vacationing outside.