Everything has risk, including an invasive operation such as sleeve gastrectomy. The risk depends on many things, including your age, sex (riskier for men), number of comorbidities, and degree of obesity. The good news is that this risk is very small for most people; well under .1% or 1 in 1000. It's lower than the risk for gallbladder surgery or having a baby.
But most importantly, it's lower than the risk of NOT having the surgery and staying fat.