In Captain America: The Winter Soldier the main plot was that S.H.I.E.L.D was really just a front for Hydra the Nazi deep science division from Captain America: The First Avenger. And they had a project in place called Insight. This was basically a plan to launch 3 next generation heli-carriers equiped with Stark's repulsors so when they go up, they never have to come down.
These heli-carriers had the capability of reading the DNA of anyone on Earth, even if they're indoors. And the only way to disrupt this ability is to switch out one of the targeting blades on all 3 carriers. Cap ends up completing this, with only 1 second to spare obv. So my little "What if" article is about what would have happened if Cap somehow didn't replace that last blade in time.
Jasper Sitwell mentions that Hydra's targets include but are not limited to Stark, Banner, and Steven Strange (Doctor Strange). And during the targeting sequence, it shows Hydra locking onto Stark, but it is implied that Banner and Strange were somewhere in there. Now we know from The Avengers that if Banner were to be shot while not in his Hulk form his body simply transforms instantly and he isn't harmed. Apparently, S.H.I.E.L.D was not aware of this, if they were then they might have taken better precaution in trying to kill him. If the shots were fired, Banner would transform, avoiding death and most likely find the source of the shooting, and destroy all the carriers therefore foiling Hydra's plans for the most part.
Now, when they targeted Stark, he was in the tower formally known as Avengers tower, previously known as Stark tower. It is hard to say exactly if Stark would die or not. The weapons are capable of killing people through buildings obviously. But lets just say he would have died for the sake of this article. What then would happen to lets just say Ultron for example. Stark had to have had either plans or had the design for Ultron finished by now. Would he have only tried to take over earlier? or would he never have been created? Hard to say really, at least until The Avengers: Age of Ultron comes out. If he did survive somehow, for all we know he may have been in his armor at the time and not been affected by the blast. Would he then fly to help Captain America? Who knows how many suits he even had, being that this takes place after the events of Iron Man 3.
Now, this will be the hardest one to speculate on. We don't know much about Doctor Strange or how Marvel will make him different from the comics. But i think it's safe to say he would die and the events of his movie would have never occurred, not really affecting the main crew as far as we know.
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