I guess I was thinking It would keep living and then give fruit next summer if we covered it with a bag at night or something in the winter, lol. Ok, i just read up a little and see that it's looking more doomed because winter is coming. Oh well, not giving up yet though.
Ok. You seem very attached to that plant and willing to put in the effort to keep it alive over the winter.
No promises, but here's what to do.
1) Give up any hope of more tomatoes this year.
2) Cut the plant right down to soil level, the way you would with many other perennials, cut down any growth that emerges before December.
3) Move the plant to somewhere cool but frost-free during winter, giving just a half cup of water when the pot is very dry. (A frost-free garage is good)
4) In March, when it starts to emerge, bring it into the light and topdress the pot with a handful of chicken manure pellets (NOT raw chicken manure, you'll burn the roots) and a small handful of woodash if you can get it, and resume watering like you did this year.
That's your best chance of avoiding disease over the winter.
