The Super Bowl winning coach might be the only guy who has guaranteed job security for next season. Otherwise, you could go 0-17 and somehow keep your job or lose in the Divisional Round and get fired. It really comes down to the specific circumstances and the owner.
That said, definitely would not want to be Aaron Glenn. Being the HC of a bad franchise is a perpetual hot seat because management is going to be impatient and/or incompetent.