I will go out on a limb here..........UH, NOOOOOOOO...
IMO, the only way Carl leaves is to be a HC somewhere. Being a DC under Bo isn't a bad gig for him. I would say in some "circles" within Husker Nation, Carl is more popular than Bo.... He is the DC (co-of course...and we know Bo calls most of the shots) and he is also the "whipping boy" for Bo....so he gets some sympathy from the fan base..
The fact that it is TEXAS also plays a role here....with the recent history, the statement that BLOOD is thicker than water (and money) will apply here.