I think people in general are a little apprehensive about change. I felt the same way as you do when Cowher took over for Noll, as I grew up with Noll as the Steelers HC. Cowher put those fears to rest quickly and I grew to admire and respect The Chin over the years. I had the same apprehension when he announced his resignation from the Steelers, but Tomlin impressed me so much in his first press conference that those butterflies in my stomach flew away and my confidence in Tomlin soared as the weeks have gone by.
The Noll era was phenomenal, the Cowher era was awesome, and I believe in my black and gold heart that the Tomlin era is going to be the wildest and most exciting ride this organization and we as fans have ever experienced.
I forget which analyst posed the question to Cowher, but he was asked if he was considering returning to the sideline next season and he emphatically replied "no". He went on to say that he enjoys commentating and he had that twinkle in his eye, so I would assume he is very content with his analyst role.