While I do mostly agree with you (we both discussed this in another thread yesterday) ... let's just say (playing a hypothetical) 4-5 years down the road, Miles gets an itch to coach elsewhere (again, not saying it will ever happen). What would be his logical "step up?"
Regardless, Nebraska may truly be a destination school for Tim Miles, for all of the reasons you've already outlined. And yes, you're correct ... the "blue blood" schools typically have a blueprint for their hires. Though that doesn't mean there couldn't be an exception to the rule. Let's just say, playing another hypothetical, Bill Self decides to bolt for the NBA in three years. And let's just say, NU has appeared in a couple of Sweet Sixteens by then (for the Huskers, that would be an insanely good accomplishment), it's certainly possible Miles could be on their radar.
Also, this is far from something we seriously need to consider at this point. As incredible as Miles has been this season, you'd like to see him play this out -- with more improvement -- for at least a couple more seasons before beginning to worry. And yes, I don't believe there's ever a need to throw lifetime contracts at any coach. If Miles wants to stay in Lincoln, Nebraska will make it work. If he doesn't there's only so much any school can do.