If you mean Elliot being dead: Esmail saying "Goodbye friend", (which was the first time it was referenced, we always hear "hello friend") as he injected him earlier in the season and the fact you can never trust what you see. Made me think of An Occurrence at Owl Creek Bridge.
In the story, a man is captured by enemy forces and is set to be hung(not grammatically correct, but it sounds better), he escapes as he's being hung he then goes on a journey and sees fantastic things, but in the end the rope snaps and none of it actually happened, he dies.
If you mean older Elliot: throughout the series there have flashbacks, everyone in the flashbacks has been accounted for in the boardroom, except for older Elliot, who was always carefree borderline psychopathic in his mannerisms, perfect personality for someone who shrugs off Vera's crazy ass.
Also, Esmail stated in an interview that the personality has been there since the beginning. That could cover all of his personalities, mother, father, younger version, slightly older, and himself.
Curious what made you think of that theory