Steve and Tony on Vormir wouldn't work
So many prop-Tony writers put Steve and Tony on Vormir, usually with Steve begging for forgiveness and plunging to his death. (Or giving up the serum, which has its own problems.) I don't think it would work. Tony isn't giving up someone he even likes, much less loves. And Steve has shown time and again he's not all that in love with life or the serum, so his attempt to sacrifice wouldn't work. And I'm not so sure he'd trust Tony to finish the job of saving the universe.
***
Of course Tony blasted off without Steve, who was forced to make the steep climb step by step. When he reached the top, he saw Tony waiting, along with someone strangely familiar. Steve asked the floating figure, "Johann Schmidt?"
The figure focused on Steve and said, "Steven, son of Sarah. It has been a long time."
Steve straightened and said, "We're not here for a fight, but we need the stone."
Schmidt said, "As I explained to Anthony son of Howard, the Soul Stone is not grabbed or stolen. You must exchange something you love to acquire it."
Tony gestured for Steve to come closer. Steve walked over and asked, "You got an idea?"
Tony nodded. Then when Steve was close, he pushed Steve over the edge.
At least, he tried to. Suddenly Schmidt grabbed Steve's arm and pulled him away from the edge, while kicking Tony off.
Steve used his other arm to grasp Schmidt's shoulder. He asked, "Why did you do that?"
Schmidt replied, "Because I knew Anthony's action would not succeed. He has no love for you, so sacrificing you would do nothing."
They leaned over the edge. Tony's body lay at the bottom, a pool of blood growing around his head. His face was frozen in shock.
Steve bit his lip, then said, "I don't think sacrificing Tony works either. I can't say I loved him, or even liked him very much."
Schmidt nodded. But then he turned to Steve and said, "It took me many years to truly understand power. But you always have, as Erskine must have known you would."
Steve held still as Schmidt laid ghostly cool fingers against Steve's cheek. Schmidt said, "I could find a way to keep you here with me always. But that would dishonor my respect for you. So I sacrifice my want, my need for YOU, so that you may take the stone and fulfill your mission."
Steve felt the brush of cool lips against his own, then everything went black.
***
He woke up in a pool with the stone glowing nearby. Steve carefully put it in a pouch on his belt, then looked to the cliff high above.
Schmidt raised his hand in farewell. Steve heard Schmidt's voice whisper in his ear, "Do not be so foolish as to return, Captain. Your companion's body will not be here. Nor will I."
Steve nodded, bowed to Schmidt, and then turned to make his way back to the ship.
He wasn't sure what he would tell the others--lie about Tony's "sacrifice," or tell the truth about Schmidt's.