Relationship with employer going south

I've been working at a bulge bracket for a number of years under a very senior MD (lots of relationships - albeit shallow ones, TV talking head, etc). This person has always been painful to work for, but as of a couple years ago, he became detached from work for unknown reasons and very focused on pursuing external opportunities on the side. For some reason, higher management has been aware of this but kept this person in a position of seniority with a small staff doing the core work of the team. I have raised concerns to HR and higher ups about the lack of management, lack of meritocracy and various compliance concerns about this person's activities. While getting a sympathetic reaction, the line of reporting of the team has shifted a couple times (indicating passing of the bucket). Six months ago, another shift occurred and it seemed this time that the next-level manager was going to be serious about imposing order. Instead, I have learned that our entire team will be shifted again to another line of business altogether with a very vague firm-wide mandate. This has been presented as a done-deal and my boss is painting it as an elevation, but it's clear that we are being banished to obscurity. When I suggested that this new direction was not consistent with my career ambitions, my boss said that I wouldn't be forced to go along with it..the implication being that I could quit. I am irate and feel that there are serious issues with my boss' behavior and integrity that nobody is acknowledging, and it's offensive that such a major change would be announced in this take it or leave it manner. It's effectively a termination of my role as it exists, yet I haven't been offered severance or another option.

How aggressively should I address this situation with HR/management? Do I need to consult an employment lawyer?