What do you mean by not working? Do you mean regaining weight, or not losing?
Well, gastric bypass is ONLY a TOOL to facilitate weightloss, so, yes, if you misuse your pouch, the surgery will not succeed, and there have been people who have misued their pouch, and the result reflecting that. That's why you need to follow
the Pouch Rules for the rest of your life, once you have the surgery, and your stomach is reconstructed into a small pouch.
In other words, so long as you abide by the rules and instructions your surgeon sets up for you, you will not fail, you will succeed.