Here a good article about Martinez, we have to remember he only 39, the same age when Moyes joined us. For those who are worring about him taking wigan down, this article says Jurgen Klopp went down with Mainz in 2007 and resigned 12 months later having failed to earn promotion back to the Bundesliga. However, his impact was such that Borussia Dortmund appointed him manager shortly afterwards; fair to say matters have subsequently not turned out too badly
Wenger got relegated at 39, too. So did Royle.
If the manager's good enough he can bounce back from stuff like that.