In all honesty, this really doesn't bother me all too much. I like CMA, but you had to expect some changes of the staff with CNS at the helm of the program. Its pretty common with the programs that he has run.
Just looking at it from CMA's point of view realistically, it's not like his offense was really given a chance to operate at it's full capacity; and dealing with a guy like CNS may not be worth the pressure and scrutiny if you don't have complete control of the offense. In other words, if you don't have final say in whats going on you might as well find a situation where you won't be judged as if you did.
I'm not saying that's what happened as if I have some inside information, but I've been in similar situations and this seems awfully familiar to me. In those situations for me, the conversation usually went along the lines of me saying "you hired me to do a particular job, if you're not going to allow me the freedom to do the job the way I need to, one of two things are going to happen. #1- I need to stop taking the heat for decisions that are not mine or, #2- I'm need to find somewhere else to be.
To add to it an opportunity comes up with his alma mater (which makes the transition, I guess the best word I can think of is excusable) in a place he's comfortable and with a culture that he knows and is comfortable with. It becomes an easy move to make, you would also now have a job title that actaully fits the level of responsibility that he's been given.
I still think CMA has a bright future and will be a really successful head coach, but it may be at Texas instead of UA, only time will tell. But for now we don't need to doubt that CNS will competently find someone to fill to OC role, the man can draw seriously talented coaches and players to his programs and in the end we will have some if not better than CMA at least equally as good. I like CMA, but hey, the SEC is a high stakes game and sometimes people you like can't stick around. I interested to see where CMA is in five or six years, and I wish him the best of luck.