I think it depends on several factors, but if a low level Bob runs out of physical and mental strength "and" his mood bar is in the red, he will crash. This might not matter when he's in an overpowering car and has an insurmountable lead. However, it's possible that he'll lose that lead unless you babysit him. Sometimes some of the AI will increase their lap times as the race progresses; so, many of us have give Bob the keys to the car, seen him build up a lead. But, when we come back, he's behind one or two cars. On the other hand, I've found that a higher lvl Bob can drive fairly well with no physical or mental strength --and balding tires-- for a while. That's why I think people can put a single Bob in a 24hr race --"Bob don't care."
I've re-entered some of the races where the max number of Bobs is 2. I entered 2, but Bob#1 did the 20 laps on his own. In fact, I don't think the AI pitted either. I ended up redoing the race with Bob#2 in the seat --because I didn't want him to feel neglected.
