One of the great mysteries of football is what role the assistant plays behind the scenes. We have very painful memories of what happened when Howard Wilkinson left to manage Sheffield Wednesday in 1983 (one of the most pivotal moments in the club's postwar history, especially given the subsequent appointment of Fat Larry). Conversely, I seem to recall a turnaround after Dennis Booth was sacked as assistant under Big Sam in the late 1990s. Even better, "Agent" Booth then went on to do sterling work as David Platt's assistant across the river.
Cox never sounded like the brains of the operation when I heard him in pre- or post-match press conferences, but time will tell. It's important Ardley gets someone he knows and can trust, because I'm sure it feels like a very lonely job otherwise. Presumably he'll need a new flatmate, too, with Cox departing.