The Chicago Bears of late have struggled to match the dominance of the 1985-1988 Bears teams that won four consecutive Super Bowls (XX, XXI, XXII, and XXIII), partof their six titles (they also won Super Bowls XXV and XXVI). Perhaps the biggest reason was the dynamic between head coach Mike Ditka and defensive coordinator Buddy Ryan. The two remained together in Chicago until both stepped down after 1992, when Mike Singletary retired.
However, Buddy Ryan could have left much sooner - he reportedly was offered the Philadelphia Eagles head coaching job that opened up after the 1985 season, but passed on it.
So, here is the question... would the Bears have won six Super Bowls if Buddy Ryan had left?