Never came across the situation but would definitely stop.
Actually, I was driving someplace the other day and saw a guy changing his tire. I think I was on my way to pick up my kids at the babysitter. It was evident he had things under control and there was a gas station about 100 yards away where he could fill the tire if needed. I figured there was nothing I could do for him that he wasn't already doing and since the kids were waiting for me... If he looked stranded or helpless, I would have offered to help him for sure but this guy was already putting it back together.