We have enjoyed unusually warm weather for this time of year. The expected cold did not arrive and our summer plants kept on growing and even flowering. If you really like the flavor of the tomato you have, you may wish to keep it going awhile longer.
I have Giant Cherry Tomatoes flowering on my table-top garden and they probably won’t set fruit but I will give them encouragement by shaking their stems. This is a good practice in normal times and some people use an electric toothbrush to vibrate the flowers. Shaking the stems calls for being gentle, almost as if you were duplicating a light breeze.
If I am successful and the flowers set, the plant will need to be protected from the oncoming cold (not only a killing frost but a slowness of growth). Take off any covering fabric when you can feel the warmth of the sun and put it on again before the sun goes down. Repeat this chore with optimism.
If you feel this is not worth doing but you have an excellent tomato variety that you want to preserve, take 8-inch cuttings and grow them in a glass of water in the house near to a sunny window. They will root readily if you change the water often and you will have trans-plantable plants for the spring.
Another attempt to keep your tomato plant alive may also be attempted. Cut the plant down to just above ground level and protect the roots by covering with a heap of well-rotted compost or even straw.
If you have lots of green tomatoes on the vines, they can be removed and ripened in the house by placing them in a single layer on a tray so they are not touching. They will ripen slowly. Or you can take the entire plant with tomatoes still attached and hang it upside down in the garage to ripen.