I don't think one season is enough unless the O is prolific on historic levels... If he turns Tannehill into something and the offense is consistently good for 2 seasons, I think he will get an HC gig.
Unfortunately it would be with some other team. If the team enjoys that kinda success, that certainly means playoff runs...and Ross would NEVER let Philbin go then. It'd be like,
Ross: "So you think we can easily fill his spot?"
Tannebaum: "Oh hell ya, just bring in that QB coach from the Jets!"