In my experience tomatoes are done at this time of year -- even if you keep the tomato plant from getting killed by frost, tomatoes won't ripen on the vine. I'd pick the green ones and be happy you had a successfuly tomato year.
I have a thriving tomato plant in a pot on my patio. It has a few green tomatoes at the moment, and a few flowering buds. But it will get down to mid-30s this weekend. Should I just pick the green tomatoes? Bring it inside (and deal with any bugs) or put plastic over it?