6 month diet

I have a question abot the 6 month medically supevised diet. I just went to my PCP this week and he is supportive of my decision to get the LAP-BAND®, so I am beginning the 6 month diet. I really would like to lose some weight before the surgery and I am motivated to try and stick to a diet. I am 5'2 and weigh 277, so I have room to lose quite a bit and still be over the required BMI. My question is--say I lose 40 pounds. Will my insurance company deny me because I have proven that I CAN lose weight? Of course, I can lose weight, but keeping it off is a whole other problem!