Other than being a link to the glory days, what have you seen that makes Parella worth two cents?
No matter what Diaco does, Parella would still be in position to teach the DL technique and attitude. When these teams have been running through Nebraska, they've been running through Parella's linemen. When opposing quarterbacks throw flatfooted under minimal pressure, that's on the DL, too.
Maybe Parella does fine with the same talent and a fresh start, but you could make that argument for everyone.