Odds of Hanging On
The days of Sparky Anderson and never-ending tenures are over. There aren't many managers who spend three decades in the majors. But success is job security; if you win you'll have a job; if you lose you won't.
You might get a second chance if people like you and your career as a player made you legendary (paging Bobby Valentine), but if you put together a solid track record of not-winning, you'll find this to be the least secure job in the world.