The skin eventually shrinks back, but the more distended it was the longer it takes. It cases of extreme weight loss (150+ lbs.) people often have a "skirt" of skin that hangs from their midsection. I think that it too will retract, but it would take a long time and surgery may be preferred at that point.
With this post, however, I don't really know what I'm talking about and going from anecdotes and the Discovery channel.
