If you look at before and after photos you will notice that people who before weight loss had a lot of fat on their face, after weight loss that fat has gone. Their face isn't saggy with loose skin as other parts of their body may be.
I think it is down to the fact that the face is always moving as it were - for instance talking, expressions, eating etc so the jaw and face muscles and chin(s) are moving. I think it is that that makes a face slim with no sagginess, and perhaps body exercise as well as masage should be started as soon as medically advised after surgery.
As to the type of exercise, I guess only a professional trainer would know what is best, or perhaps a surgeon in a follow-up clinic could advise. That is just my take on it, but not sure whether exercise would help, and I suppose it is genes and age that may be the answer.