His best bet would have been to backtrack by the route they followed in, assuming he could remember the turns that got them there. That would have kept him on roads, more likely to eventually encounter another vehicle, and ultimately, get him back to the main road. If he ventured into that creek/valley as the current reports suggest, and into an area with large cliffs, etc., I think the odds that he is still alive are extremely low. Given his attire (jeans and sneakers, no hat, as far as I have read, combined with cold and damp), hypothermia would have taken him down pretty quickly.
But miracles do happen, and maybe he has managed to survive somehow.
Earlier in the disaster, he should have been able to follow his tire tracks...even if he could not remember the turns that he took.
Traveling cross country can be very tough physically and mentally...even for experienced, well conditioned, and well equiped folks. Even in my youth, I rarely would try to jump over all of the dead fall, etc. with a full pack.
When I heard that he left the road for the river and the cliffs...with no hat nor any gloves...wearing cotton pants...I was very worried for him.