After another 12 hours passed it was apparent no living survivors would return to the area. It was going to be difficult for Pappa to operate without assistance so he knew it was only a matter of time before he would either "bunker" in place or egress away from it.
more time passed before he felt that the wall where closing in on him.
Going topside of the train and working on the UAV to get ready to launch. This would be the best way to gather intelligence without disturbing the dead into activity or a frenzy.