Hmmm... this differs with anyone, it all depends on your shape, ages, how long the skin has been stretched, skin type, what you eat, drink... there's so much to factor into it that there is no definitive answer to this.
Obviously exercising helps, however once skin is stretched*, no matter what you do it's not going to go back... *depending on all those factors above.. It's a tricky one, and something we all have to face.
I remember when I lost a lot of weight about 6 years ago, I my tummy was just like i'd had kids...this time, I expect there to be a big difference as I've had another child since and my weight has changed.. If there's going to be a problem, it will be around my front (my legs aren't fat at all, my my inner thighs are a bit, but nothing to worry about... to be honest, I think you have to look at what's worse, lots of unhealthy weight or a bit of loose skin? To be honest, If I do get a lot, and it makes me miserible, without a doubt I think I'd go for surgery.