If your insurance covers bariatric surgery, they should cover the laparoscopic adjustable gastric band. However, they will not cover it for patients with a BMI of less than 35. And, they may not cover adjustments of the band, especially if you lose coverage for bariatrics. Medicare only covers adjustments once every 90 days.
Note that you will have copays and deductibles. Note that most insurances also have additional requirements for approval for surgery, such as 6-months of physician supervised diet, 3 years of primary care physician records, and psychology clearance.