Then he'd be manager of two teams that got relegated within three years. Even Neil Warnock never pulled that off. That's Paul Le Guen-level failure.
If he got us relegated, Martinez might have trouble getting a sniff from a League 1 club.
Actually Avram Grant was in charge of 2 teams that got relegated in 2 seasons - Portsmouth one year and West Ham the next, although to be fair Portsmouth was a sinking ship and West Ham were pretty much on the decline as well.
I wouldn't be too worried about Martinez on a career level if things ended badly with him here, judging by our performances in the Europa League, a few European clubs might be interested, I could see him even manage a mid-table Spanish Primera Division team. Otherwise, he could form a very solid career as a football pundit on TV.