I think JarodRussell
is laboring under the notion that there is only one degree of "dead". There's dead as in the heart has stopped and ain't about to start again without intervention and then there's brain death...and I think brain stem death too. Legal and medical definitions have shifted over the years as medical science pushed back the point of no return.
But yeah, regardless this is a comic book show. Bringing a person back from thoracic trauma and a spymaster garnishing the truth of his prognosis is a lot more plausible than a some magical serum that doubles a person's bodymass, makes them bullet proof and allows a human body to survive more than half a century in a glacier.