If I were a head coach (scary, huh) and saw that on weekly basis my offense was under performing and I had years of experience as an OC, I would want to take over the reigns. The performance of this team and it's coaches is ultimately Mussman's responsibility.
I use the New Orleans Saints as an example of a head coach who has an offense driven mind. Payton defers all of the responsibilities of the defense to Gregg Williams, but Payton runs the offense. He has an OC who assists him, but Payton calls the shots. Here is an article from last year in regards to the relationship the Saints OC has in the overall scheme.
Ultimately the success or failure of Sioux football rests on Mussman.