There was a second timeline where they all won, but Stephen was absolutely against it. The problem with both winning timelines though was that they were damn near identical except for one single choice.
A choice made during the second battle with Thanos.
If he were able to tell Tony, he was positive that the genius would agree that the second timeline was not an option.
But no matter how hard he tried not to let it happen, the dread that filled him in the middle of battle was his answer to his ignored prayers. He was going to lose the one thing that was truly important to him.
"Foolish child. I am inevitable."
Stephen turns his attention from the waterfall just as Peter's arm lights up from the power of the combined infinity stones, and the sorcerer nearly sobs at Tony's desperate protests from across the field.
"Yeah? Well...I'm Spiderman."
Peter snaps just before Tony reaches him and a bright light flashes across the battle site. Thanos and his army turn to dust, and the cascade of water Stephen's keeping at bay ebbs away, giving the sorcerer the opening to rush to Peter's side. Tony reaches the boy first and catches his collapsing body before gently setting him against a wall, and he kneels in front of Peter as Stephen joins them.
"Peter?"
Recognition flashes in dulling brown eyes and Stephen falls to his knees beside Tony. "Why would you do that?"
Pale lips tremble. "Didn't...want to lose...another parent."
Tony leans forwards and gently rests his forehead against his son's with tears freely falling. "You did good kid."
Stephen smiles despite his own tears. "You deserve a nap Spiderling. I'm sure you're tired."
Peter tilts his head. "...just five minutes."
The moment Peter closed his eyes, his final breath left him and only then did Stephen release a heavy sob. Tony turns to him with angry words ready but his words die in his throat at the sight of the doctor's pain. Brown eyes meet blue, and the latter looks down.
"It was supposed to be you."
Realization dawns on the engineer, and he reaches forward to bring the sorcerer into his arms.
The silence that followed was deafening.
Mama Bear's cub was dead.
And Tony Stark had to watch his son die a second time.
Except this time, there was no getting him back.
A/N: This is a really twisted version of Peter saving Tony and Stephen. Please don't kill me. It's mostly a what-if situation, hence the shortness of it.