What if Coulson did die and he's now a robot?
Life Model Decoys are a popular plot device in the comics used by characters including Tony Stark and Nick Fury. In The Avengers, Stark mentions Life Model Decoy as a joke to Coulson when he comes to Stark Tower, essentially confirming that Coulson at least knows about Life Model Decoys as if they're part of S.H.I.E.L.D. or at least present in the Marvel Cinematic Universe.
We can't say that it was a Life Model Decoy that Loki killed in The Avengers, because of the blood, medics and genuine concern for him... or maybe we can?
Verdict: Nah, this would be too obvious.