Unless he's a mountain man, or had an accomplice following in a different car, he's not disappearing from the Craig Pass area. That's one of the most remote areas of the park that's accessible by car. He'd have to walk at least six or seven miles down the road, even farther if he went into the back country.
If the car had been found near a busy area such as Old Faithful, I might consider the possibility, but there's little if any public transportation in Yellowstone at any time, and this late in the year, most of that is shut down. Somebody trying to get out would have to bum a ride with somebody or arrange for somebody like Karst Stage to pick him up. He'd likely be remembered.
