Hi, Karen, and welcome.
Revising RNY gastric bypass to the DS is a very complex surgery with significant risks. There are only a handful of DS surgeons who do these challenging revisions, and none in the Boston area.
However, if there is no surgeon doing this operation in your network, you can request authorization to go out of network. It isn't your fault of no one in network does this procedure. The real issue is going to get approved for this operation at all. What you need to do is get your Evidence of Coverage (EOC), a lengthy document, usually more than 100 pages, that provides all the specifics of what is covered and what isn't, and what criteria you need to meet for revision bariatric surgery. These criteria are often different from those for a primary bariatric operation. Never, ever rely on some random employee over the phone who says you are covered. You need to read the specifics yourself. The EOC can be obtained through your HR dept if your insurance is through your employer, though what often happens is that the folks there have no idea what you are talking about and you need to speak with managers, supervisors, etc and persist until you find someone who has a clue. If insurance is through your spouse, you go through spouse's employer.
There is a lot of good info in the "insurance" section in a sticky
DianaCox wrote awhile back.