This may be rather naive but won't your skin tighten up after a while, it's been stretched for a number of years so it seems common sense that it might take a good time to get tighter.
SP, it depends on a few factors. Age is one-- younger skin is more elastic and will tighten back up. How overweight you were and how long you were overweight for affects it-- it's easier for skin to tighten up if you've only been slightly overweight and/or for only a short time. Genetics help too- some people just have skin that tightens up more easily than others. Losing weight quickly can affect how your skin fares as well. It's a good idea to lose slowly so that your skin has ample time to get back into shape slowly. Also, losing weight fast usually means losing body fat over muscle mass even if you exercise, which can leave a lot of subcutaneous fat.
There's some controversy about whether these skin removing surgeries and tummy tucks etc. are actually necessary for most people because proper exercise and losing weight the right way talk care of a lot of these problems naturally. I spoke to a personal trainer friend about this who is of the mind that a lot of this surgery is unnecessary and also not permanent-- if you get your body fat to a healthy percentage, stay in shape, and be patient, you're better off and will have lasting results.
With that all said, if my fucking c-section scar is still all weird once I'm done losing weight, I'm calling my friendly neighborhood plastic surgeon.