Question is, how much does he play with the defense.
One thing I love about Saban and his "control freak" mentality is that no matter who comes and goes, it is a Saban team. The OC gets to add/tweak about 30% and do what he wants, but all in all there is not a huge drop off in system/terminology when changes take place. Prime example was Applewhite going to TX and McElwain coming in.
Does Petrino do something similar or is this going to be a start from zero type thing? Either way, that much transition can't be good.