Doesn't matter how conditioned one is, what will he do when he gets to the 50 mile mark - that is if he can even get past the government guns and zombies? Best to stay home.
It is sometimes amazing what an out-of-shape coach potato can do in extreme circumstances. Take this example of a sedentary person who’s 100 lbs. overweight. If it’s extreme cold weather, then all that extra blubber will certainly act as effective insulation. It’ll also keep our theoretical refugee fed for a couple of months. So what if he can only manage five or ten miles per day, he’ll get there eventually. I, with my low body fat, had better get to safety quickly before I starve to death.