Les Miles is not a great defensive mind. Prior to becoming head coach at Oklahoma State, his jobs were always on the offensive side, including offensive coordinator. He's 63, which doesn't disqualify him.
Jon Gruden, whose name comes up for every job, would be a terrible choice as a college coach. He hasn't coached college football for nearly 25 years. Imagine him dealing with NDU's rules and culture.
Charlie Strong would be a great defensive coordinator for Notre Dame. His personal issues, involving a Louisville donor's wife, could stand in the way.
Mike Gundy has become a very good head coach. I believe he would be willing to move--he seriously entertained the Tennessee job before Butch Jones--but whether he would move to Big 10 country? Larry Fedora and Todd Monken were assistants under Gundy.
The Notre Dame fan base may not find it palatable, but hiring one of the fine coordinators out there may be a smart move. Tim Drevno at U of M is well qualified to be a head coach, though he seems married to Harbaugh. Sonny Cumbie at TCU is a young, brilliant offensive mind. Brent Venables, defensive coordinator at Clemson, is ready--he coached and played under Bill Snyder and coached under Bob Stoops; Clemson's defense.... Mike Sanford: he's soon going to be a head coach somewhere.
If someone with P5 head coaching experience is demanded, there's Stoops. Not Bob--he's not taking another college job--but Mark. He developed Florida State's defense and has resurrected Kentucky's football program; Kentucky beat Louisville and Lamar Jackson on Saturday. He's recruited better than any coach in Kentucky's recent history (Bear Bryant, 1946-53, may have done better). Stoops is from Youngstown and Catholic, of course; he would fit Notre Dame.