I dont think that they will be pleased, but I also wouldnt expect them to be jumping on the bandwagon with you either. A lot of times that kind of thing doesnt give us the satisfaction that we expect.
If he does contuinue contact with her, it is extremely disrespectful! I would lay down a boundary, "I will not share my husband, what you are doing is disrespectul to me and our family" and then expose away! You may be able to bust the affair, but whats really going to turn his head is the 180's and the GALing. Have you looked into what kinds of things there are to do where you are moving?
I guess I gave the wrong finger to the wrong man...