I doesn't matter who the coach is next year. Alvin and his brother chipmunk's should be able to coach a NFL team to the playoffs with the Lions 2016 schedule. If Caldwell Wins he stays. If he doesn't he gets canned.. Quinn is in a no lose situation. If the Lions fail he cans the head coach and takes no blame. If we win he is lauded as a genius who listen to his 90 year old owner and kept Caldwell.
This move is about getting Calvin Johnson to stay another year I think..
While I don't disagree with anything you said here, I do not think the Lions miss the playoffs next year even if CJ does retire because the schedule is very much in their favor.
I also do not think having CJ enables them to win a playoff game next year.
Their only shot at winning a playoff game, IMO, is if their opponent had a strong start to the year but then got hit with multiple injuries, including both their starting and backup QBs, and limped into the playoffs without any of their star players.
Even then, Detroit would need homefield advantage. Even then, I put their odds at best around 50-50...provided opponent had the entire team come down with the flu.