Lots of questions here, I'll try to hit the high points.
Yes, get a copy or disc of the upper GI, and ask the radiologist specifically to assess the size of the stoma and not just the size of the pouch. Everyone seems to focus on whether or not the pouch has stretched out and ignore the stoma. In reality, if the stoma has enlarged significantly, it doesn't matter how small the pouch is, everything you eat just falls out of the pouch and into the small intestines, leading to near constant hunger, and, of course, weight gain. This can also cause dumping and reactive hypoglycemia.
Regarding your insurance coverage, never trust what some random employee tells you over the phone. It's crucial to know the specifics of your policy. Even if that person is right that revisions are covered, what type of revisions? Under what circumstances? There are often very specific and more stringent requirements for coverage for a revision than for a primary bariatric surgery, AND you need to know coverage for the DS as well, AND you also may need to know your appeals rights, if any. So get that EOC - no one cares about this as much as you do. And if the policy is confusing, there are people here who can help interpret it, but only if you get it.
Regarding dumping, the milk issue is not dumping, it's lactose intolerance. And we get it with the DS too, so that probably won't change. And most bariatric surgeons believe that dumping is a side effect, and not a complication UNLESS it's like the dumping
@Kristaz had where the foods involved were healthy foods (not sugars and/or fat) and impairing her health. If you are having sleep issues, get tested for sleep apnea, because that's a serious comorbidity that could help you get approved for revision, but I really don't think the dumping will do it. But hey, I've been wrong before, and Dr. K will be the one trying to get authorization, not me, so make sure he knows about it and we'll let him sort out how serious it is.
You were told the gastric bypass is permanent. My interpretation of that is that what you may have been told was that the operation is permanent, not the weight loss. Most RNY surgeons tell their patients to consider the operation permanent because it's so difficult to reverse and reversal is so rarely done. But most also tell their patients that if they don't follow the prescribed diet (low calorie, low fat, low carb) they will regain weight.