Mattison left Florida recently to be the Ravens DL coach, if I'm not mistaken. Definitely sucks for us in the short-run, but two coaches who got no real interest in a year of tons of college head coach openings leave to the NFL to showcase their Xs and Os.
Sherman left A&M not long after being promoted to A&M offensive coordiator, and his career path took him to an NFL head gig. I think the logic says Herring got as high as he would in the college world and the NFL holds a brighter future for his "Xs and Os" mentality, at least that's what he thinks.
Best of luck to him, and hopefully Johnny Holland comes to College Station.
Plus, I'm sure Jerry sold Herring on more of a future than being the current linebackers coach.