Some do, some done. This is 100% a case by case thing. For me, I had gallstones before bypass, so I didn't need to take any of the gallstone medication. My stones were not severe enough to warrant removal of my gallbladder. So far, just shy of 6 months out, no issues with my gallbladder. So, if things keep working out this way, I won't have to have it removed.
But there are folks that do have to have it removed during surgery and some folks have to have it removed after surgery.