Let me throw this out there. Jim McElwain is the HC at Colorado State, his team finishes the regular season 10-2 and is headed to a bowl game. He leaves and immediately starts recruiting at UF, his new employer. Why shouldn't he have to stay and finish the season out?
Will Muschamp is "fired" but allowed to finish the season. UF makes a bowl game but he isn't allowed to coach it, instead an "interim guy" will. Why can't he stay?
Any OC or DC that aspires to be a HC must go and start laying his foundation immediately at his new school. If he wants to succeed, he will leave immediately. When I say succeed, I mean win 5-7 games his first season and show improvement. Use the Houston job as a stepping stone.