There will be casualties on both sides if this should come to pass. I think ultimately, the citizens would win. Law enforcement is accustomed to outright resistance by "citizens" (as opposed to dirtbags) who vehemently resist. If and when the casualties start to take place, there will be a rethinking process.
I'm particularly worried about young cops, who see it as their role in society to be "avenging angels"; "the law" and the ones who will decide who is right and wrong. It takes an average of about eight years of real, full-time experience to make a good cop. Some make it quicker, some never make it. Just like the rest of us, LEO's have to mature. If you look around you and try to evaluate the personalities of family members, neighbors, local officials, etc. you will note that there are varying levels of competence, maturity (or call it seasoning) and general understanding of the rules of life. In this country, we give 21 year- olds a small amount of training, a badge and gun and send them out to enforce our laws. There is occasionally a requirement that the officer have college education, and that is important, but far too rare.
As I said, some of these guys and gals will side with the constructionist interpretation of the 2nd Amendment and some will follow their "leaders". All law enforcement/national security/military, etc. are dependent on government for a paycheck. That puts them in a dilemma. Do they lat out refuse to follow order and subject themselves (and their families) to termination and loss of all their material goods? Or do they follow their conscience and refuse unlawful orders? I hope that as things progress, law enforcement leaders will start to think beyond their first inclination to follow the orders of "the government" and start a sort of "guerrilla" operation in which they become extremely inept at finding the newly banned weapons.
I fear that we're about to find out.