This is an issue most of us have encountered -- in my case, several times over, including presently -- because those of us who are getting IVIG are doing so on an exceptional, off-label basis, and also because IVIG is extremely expensive -- and getting so more and more -- such that government programs and private insurance companies have a huge incentive NOT to pay for it.
(When I started getting my 90 gr/day dose in 2009, it was priced around $15,000. By now, 6 years later, it has doubled to about $30,000.)
In my case, even though I haven't changed jobs, my employer has changed insurance companies, so it's been "back to square one" each time that they do. Moreover, now that I've become eligible for government-provided Medicare as a back-up insurance, I'm in the midst of appealing their denial, and even their denial-upon-appeal, of my getting IVIG.
So yes, if you change jobs, you should expect to be denied coverage of IVIG by whatever insurance company your employer has contracted -- even if it happens to be the same one you had before! -- so the key is to be prepared to put on a good fight, namely, to increase the odds of a successful appeal.
And this is a fight that many members of this Community have had to fight -- and I know because many have turned to me for help and advice -- so consider yourself to have been unusually lucky, indeed.
Here are the ways to increase the odds of a successful appeal:
1) You have to get the physician who knows your medical history best -- preferably, from before you started the IVIG therapy -- to draft up a "To Whom It May Concern" letter making the case for why you need to remain on an IVIG therapy on an exceptional, off-label basis. (It's like getting a colleague to draft up a letter of recommendation, just in case you need it in the future.)
2) You have to get Dr. Kirk Druey at NIH to do likewise. He has done it for several of us already, and he will do it for you, too.
3) You have to put together a list of articles touting good experience with IVIG for SCLS. (This is the easiest thing: I can send you my list, which includes more than a dozen entries.)
4) If your job change will include moving, you need to line up a physician who will take you on and help you "fight the fight" and, if need be, will have you admitted to the hospital and give you IVIG on an emergency basis. (This is the hardest thing.)
The long-run solutions, of course, are (1) to find a definitive cure for SCLS, because IVIG is not; and/or (2) to get FDA (and similar regulatory approval in other countries) for IVIG to become an "on-label" medication for SCLS.
Dr. Druey is working on solution #1, and I am working on #2, but it is best to assume that either one is going to take several years to come to fruition.