If the planet is no longer capable of sustaining life after the nuclear war is over -- and I would argue that once you launch a couple of missiles you might as well launch them all, just to be safe -- then yes nobody wins. Your country/continent might die out more slowly than the other ones, but nuclear winter will kill everyone.

Now if you have 1000 years of rations saved up sure you might win. You might be the only person left on earth. But is that winning? Maybe somebody thinks so, I guess.