6. Clark Gregg - Agents Of S.H.I.E.L.D.
The Death: Onboard the Helicarrier, Agent Phil Coulson (Clark Gregg) is stabbed through the chest by Loki, who then escapes. In typical Joss Whedon fashion, a likable supporting character bites the dust brutally.
The Resurrection: Though not all the details are available as of yet, Coulson returns in the upcoming TV show Agents of S.H.I.E.L.D., though the nature of his resurrection remains sketchy. He's not brought back by way of Vision, and reports so far suggest that the mystery will play out over an entire season, with Coulson himself not finding out for a while. Other S.H.I.E.L.D. agents, meanwhile, deliberately keep the truth from him.
Why He Should Have Stayed Dead: The problem with bringing Coulson back, supremely likable though he is, is that it totally undermines the gravitas of his death scene in The Avengers. That death was a memorable, affecting moment in the middle of all the mayhem, and to essentially ret-con that for the sake of a TV show spinoff seems tacky and lazy. Though many have suggested that Coulson's death may have been faked as yet another ruse to inspire The Avengers to work together, it seems that the real trick was played on the audience. Though we'll have to see how the execution plays out, there's still very little chance of it not cheapening a key moment in the Marvel Cinematic Universe.