Then finally shows up and dies before the end.
So he might as well have died in season 1 really.
Its something I wouldn't normally pick up on - save for the fact he was in Relativity and Fury - its as if they thought that they could only get him back in the past!
They mixed Carey up with Hogan (who died in Basics) and then killed him off for no real reason.
They should've made a whole episode revolving around the idea that everyone outside of Engineering and the Doctor thought that Carey was dead and Hogan was alive, while the Engineers have to convince everyone else of the truth.