I've had this thought and pseudo-concern, but when you think about it, is there much of a successful history of "having the next head coach on staff"? Belichick wasn't on the Patriots staff before he took the job. Tomlin wasn't on Pittsburgh's staff. Jason Garrett is about the only coach in waiting situation that I am aware of and is he all that successful? Jim Caldwell did it, but didn't last. That's very true. Belichick also didn't really succeed at the Jets (he had been at the Patriots in 1996, prior to taking HC job after leaving NY). There's a few examples of guys that were on the coaching staff of a team before leaving for some other job, and coming back to that team as HC eventually. Tom Coughlin and Mike Shanahan both did that, but it's not exactly what you're talking about.