How "middle of nowhere" are we talking?
I can't really picture a situation where I would be out in the wintertime without so much as a farm house within a few minutes ride. That's probably what I would do... seek shelter, warm up a bit, then head back out. Hop from place to place if necessary.
If there really was nowhere to go, then I'm probably out touring or something, in which case... I would have brought enough layers. I did get a flat once in the rain in the middle of nowhere and my fingers were too cold to change the tire. Fortunately, it was a slow leak, so I just pumped it back up and hoped for the best. It held on for another 20 km :-).
For the most part, my winter riding is for the purposes of commuting, in the city. I even made the decision to not bring a spare tube and pump on winter rides - I'd rather throw the bike on the train and walk it home than sit and change a tire when it's -10.