Idk about tOSU post-UM, but I have a theory about BP.
He viewed the NU job as a stepping stone. I think he had a three-year plan. My evidence: 1) he had NO staff turnover for his first three years. I think he made a deal with his assistants to commit to him for three years to build NU to the point he could parlay the NU job into something bigger. 2) Bo’s own words on the post-tOSU comeback win. “...and when I’m gone...”
I think he thought he would get that tOSU job after beating Fickell that night.
But no (better) offer ever came. Ever. He had no long-term plan, so things came off the rails after 2010.
I think losing Carl also hurt him, as I think Carl had a brotherly way of keeping his brother in check. The appointment of a puppy like Papuchis to DC was a case of BP surrounding himself with yes men.