I was always told to interview for any promotion you were invited to try for, even if you knew you were not going to take it. Firstly, it keeps your interview skills fresh. Secondly, if it is something even semi-publicly known it can drive more people to look your way. Sark will want to be a Head Coach somewhere, probably before Saban retires. It does nothing top hurt his stock if it is known a school with an NC in the last 10 years (and one that has played for two in that time) is looking his way.