I agree with Damiola,
Age is certainly a factor, rate of weight loss, diet, how much weight lost and of course it takes time. And whether the weight gain was quick or over a prolonged period as well as how long overweight..
If you are young, lost the weight slowly, have a lot of collagen and cofactors in your diet and you are patient, skin can certainly recover.
However given he had bypass surgery, I am going to assume he was quite large for some time and has lost significant weight. This would most likely need some help.