You won"t have to worry about many of them - if they are truly walkng 5 mph and trying to cover 50 miles a day. Even a young healthy person would be pushed to do that more than one day. (If you doubt that, try getting on a treadmill at just four mph and see how many miles you can do!)
After that first day, everybody would be looking at their fellow walkers and seeing hamburger meat! That"s when the real fun would begin.