I think Gruden is overrated. His players hated him in Tampa, in not in that good way.
If Bill Cowher wanted to be coaching, he'd be coaching. You think the availability of the Texans job is going to pull him out of retirement? Not a chance. There are potentially going to be WAY more attractive jobs (for Cowher) than Houston at the end of this season.
Carolina - where he's from and where most people think he's just waiting for them to fire the current HC.
Dallas - huge piles of money, high profile job - and if you think he won't put up with the Billionaire Hillbilly Jerrah Jones, don't forget that Parcells put up with him.
Redskins - high profile, owner is insane with money and will spend it without question, great division, rich history.
Vikings - great O-line and D-line already in place, perhaps the best RB of our generation already in place, decent amount of history.
Look at all those jobs that might be available, and ask yourself why Bill Cowher would consider the Texans?