Hi, surgeon here. No, they do not become incontinent, which means losing the control of your sphincter. They can get chronic diarrhea,  bc  the way their guts are rearranged may  lead to mal adsorption and watery stools. But actually, that has  gotten a lot rarer as we have learned to optimize length and type of intestinal bypass. And most lose about 10% - 30%  of their excess weight. Not total body weight, mind you excess weight. So if someone weighs 180kg and a normal bmi would start at 80 kg for him, the weigt loss would be 10 - 30 kg. The good news is.. The diabetes dissappears at a very high rate.  So, at least society is no longer burdend with the costs of dealing with that.