The sweet potato's, let them go until they basically die off themselves from the frost or whatever. Also WATCH WHERE THEY GO !! From my experience they vine ALL OVER the place, and every say 5 or so feet where that vine touched ground, it'll dig in and you'll have another bunch of potato's to dig there too, don't just dig where you planted them, follow the runners.
Sweet taters love TONS of water, and fall into the category of 'Thee who I ignore Most Grows Best' plant. Just keep them watered and at the end of the season dig them then. Just let them go, see what you get out of them. I made the mistake of letting mine get out of the totes and they are now, literally growing like a carpet thru half the lawn there. Not necesssarily a bad thing but man, harvest time is going to be a bugger.
If you think they did real crappy, another option to 'calling them'... just IGNORE them, don't harvest, just leave them there in the ground. Next year they should come back with vengeance for you !!
Aaron