two big reasons IMHO to move on from Nix:
1) luring a respectable (preferably big-time) name HC to Buffalo becomes exponentially more difficult with Nix staying on as GM; it is difficult enough with RW as owner to land that big fish as HC. Nix represents the multiple failures already cited in this thread, and a top-notch HC needs to have the confidence that he can hitch his wagon to a progressive, forward-thinking GM. The dynamics of the NFL have proven themselves to change again with dynamic young QBs like RG3 & R Wilson, and these dynamics seem to be unrecognized by Nix.
2) scores of empty seats galore for the last 4 home games; it's no coincidence at all that it was Brandon who met with Ralph, not Nix. I am betting Russ sold Ralph on the idea that the fans have spoken with their absence, and he cannot make lemonade out of lemons, hence selling Ralph on the wholesale change required as a byproduct of pure economics, plain & simple.