They actually got relegated in Robles' last match, the second to last weekend of the season.
Look, the point is that no one has seen more of Robles than Roberto Martinez. He's seen him in training every day for three and a half years now and watched him from the touchline in 34 competitive matches. He doesn't think Robles is good enough to be a regular starter, even though he has every incentive to make him one. If under these circumstances he still doesn't think Robles should start, I'm inclined to trust his opinion over that of anyone posting here.