In all honesty, Tony Stark always thought he would die protecting his friends.
Not because he was a hero- because god knew that Tony wasn't a hero- but for the simple fact that he was the least important of all of them. He was expendable. If it was 'sacrifice one member of the team so the rest can live', everyone would turn to him.
(Maybe not aloud, but he knew that they would all be thinking it.)
So he envisioned himself dying in a collapsing building after throwing Clint to safety. It didn't sound so bad.
Maybe they would appreciate him, in the end.
And if not dying for his friends, then it would probably have been some form of suicide. It wasn't to say that Tony Stark was actively suicidal, (which he was, depending on whom you asked,) but that most people thought he would do something to kill himself.
Maybe it wouldn't be obvious suicide, like hanging himself or shooting himself in the head. Maybe it would be flying through a portal in outer space, just because he felt like it.
(Or drinking himself to death or flying past the limits of the atmosphere or freezing to death or or or-or-or)
But Tony could never have envisioned going out like this.
He honestly never thought that a teammate would kill him. And it was ironic, really, because his dad used to tell him that Steve Rogers was better than him on every level and he would trade his son's life for his friend's in an instant.
Howard got what he wanted. Steve Rogers slammed the shield that Tony's father made into Tony's chest, and killed him.
Destroyed the ARC reactor. (That Tony made.)
What a twist of fate. That Howard's legacy lives on with Steve, but Tony's legacy will be cut short.
What was with people and their loyalties? Howard wasn't loyal to his family, but his friend. Steve wasn't loyal to his team, but to his best friend. Why was it that right as Tony began to trust Steve, right as they became friends- why?!
Why did Steve have to do this?
He didn't even listen. He didn't read through all of the accords. He didn't listen when Tony told him that they could be amended and that he could fix them up. Steve didn't listen to 117 countries telling him that he was a time bomb, he didn't listen to the people when he decided that he was better equipped to handle everything on his own judgement.
He didn't care about anything except for Bucky Barnes. And Tony decided that he could get over his jealousy because he was dying.
He was just so fucking tired.
So Tony leaned back, into the cold Siberian bunker, and watched as Steve and Bucky walked away. They would take the Quinjet, leaving Tony with a broken suit of armour and no possible way to leave.
For a moment he wondered if Steve had planned this all along. Nobody would know. Nobody would know where to look, where to find him. He didn't care- he'd be dead in minutes. The reactor was broken. (For a moment he wished that he had tried harder to get the shrapnel out. He wished he didn't need the reactor.) For a moment, Tony wanted more time.
Rhodey. Oh, god, Rhodey.
He felt a surge of strength just thinking about his best friend, limping around, with no new tech to get him walking-
Collapsing into a spasm, Tony left the thought behind.
Jerk. Thrash. Choke.
Steve and Bucky didn't even turn around to see that Tony Stark was dead.