things can go wrong with *any* surgery. People have died getting their tonsils out. But like tonsillectomies, this is one of the safest surgeries there is. Mortality rates are extremely low - something like 0.3% for bypass, even lower for sleeve. It's much safer than a hip replacement surgery, and they do those every day!
re: getting too thin: far more people don't make it down to their goal weight than get too thin. I wouldn't worry about that one *at all*. Plus you can always stop the weight loss by adding more calories.