Here’s a weird tidbit dug up by Chase Stuart of the always awesome Football Perspective: the Tampa Bay Buccaneers haven’t had a coordinator leave and turn into a head coach since the eighties—unless we count Dirk Koetter last year.
The Detroit Lions are the only other team not to have a coordinator turn head coach since 2006—and they had that happen in 2004 and 2005, not in the eighties.
Stuart finds that only Wayne Fontes and Joe Gibbs went on to become head coaches. Both of them coached under John McKay, Fontes in the eighties and Gibbs in 1978.