I don't have enough information to conclude if keeping Bo was the right decision. if there was no good coach available, it was the right decision. Otherwise, I believe it was a mistake.
I would be really surprised if a better coach were not available --- really surprised. I think it was a mistake --- not because of the on-field performance (or lack thereof) so much so as the reputation of the football program...
Living out-of-state, based upon my seeing the perception of other football fans, when NU comes up, the response is almost uniformly the same --- they think lack of class. They think of Ritchie incognito, Bo Pelini, Carl Pelini and Suh (and, if they are older, add Lawrence Phillips in there) --- and they think very, very negatively about NU football as a result. They see temper tantrums, headset throwing, F-bomb laced tirades, angered-drenched defiant interviews, etc....
The point is, if a poll were taken nationally, and the question is what football program displays the least class... NU would be tops or close to tops in the poll. That the NU administration chose to retain a coach who has contributed so much to the negative perception of the program and the university is most disappointing. To me anyway, the poor coaching quality and on-field lack of results are secondary to the class of the program... which has been, and seemingly remains, compromised.
I see this as a mistake and speaks volumes about the AD --- and not well.