Gastric by-pass or other surgeries to lose weight. Do you know of many cases that work long term?

I personally know three people that had surgery on their stomachs to lose weight. In each case the person lost over 100 pounds but within 2–4 years gained it all back. I know one person that lost over 100 lbs and has kept it off for about 5 years now. I’m wondering if this is even a good alternative to weight loss.