IIRC
The NFL offered the Lions assistance in finding a new GM after 0-16 (the Bears accepted to this help last offseason). They (by "they" I'm assuming WCF and family) refused and decided to promote Millen's understudy (
on advice from Millen himself!). I know it's hindsight, but that decision was not greatly accepted at the time and doesn't look good at this point.
Millen was GM for 8 seasons (well, 8 drafts and 7.5 seasons), Mayhew just finished up his 7th draft. Their time served will be even at the start of next season (if Mayhew stays around), and while there's no arguing that the franchise is better off compared to what it was (how could it not be), it's still disappointing from an overall NFL standpoint. A couple good seasons scattered with disappointment, yo-yoing from playoffs to bottom tier, entire draft classes gone. To be quite honest, with the number of very high draft picks left over from the Millen debacle, a 4-year old probably could've orchestrated some kind of a turnaround, it's easier to rebound with that kind of talent available. I realize there was some bad luck with injuries, but I hardly find that a good excuse, other teams deal with that too and many teams overcome it by building up a quantity of talent, something Mayhew hasn't done well.
Unfortunately, I don't think the culture of this franchise has changed all that much. Let's be honest, when was the last time Super Bowl was even in the discussion? Even now, the goal feels like it's to reach the playoffs, anything else is gravy. That's not good enough. It's like we were so beaten down by years of losing that anything better than a losing record was acceptable. Compare that to several other franchises around the league, where even 7-8 wins in a down year is utter failure. I'm not saying we should scream for a Superbowl after a 4-12 season, but turnarounds should be quicker than 7 years, Calvin Johnson's prime should've been spent playing meaningful games in mid-January.
The big contracts of CJ and Stafford are coming up in a few years (well, cap positive) and that could give the Lions the opportunity to completely clean house. New GM, new coaching staff, flexible cap. There's no guarantee that things will change, but I feel that it gives the best chance to "reinvent" the Lions.