In some kind of Jumanji way, Tony comes back in the far future, like very far future after some kids found an infinity stone. Doesn't really matter how or which one, it's the far future so we don't know any of it cause we don't know how many things happened since Tony died and the present. So Tony comes back in a world he doesn't recognize anymore. In a world the people don't even know him anymore.
"Who are you?", one of the kids ask.
"Tony Stark".
The kids remain silent like okay, that doesn't help us at all.
"Iron Man?"
The kids: ?
"The universe's savior? I defeated Thanos?"
"Who's Thanos?"
"Isn't that a villain in a comic book?"
Tony frowns. "I'm on earth, right?"
"Yeah"
"What year is it exactly?"
"4183"
Tony stumbles.
"Wow. You're okay?"
"Nope. What city are we in?"
"New York."
"It doesn't look like New York."
"So are you like, a genie? We found you and freed you and that makes us your masters? Can we give you three wishes each?"
"1, I'm a genius but not a genie; 2, I'm the one who's gonna be giving the wishes and I want you to take me to the NY sanctum, that thing must still exist AND I want you to buy me an American cheeseburger."
"What's that?"
"You gotta be kidding me."
Anyway, they go to the sanctum. The new guy there says he can't help him go back to his time but he knows of someone who can help. Thor arrives. He's super happy to see Tony.
"How long has it been, like a hundred years?", he says as he hugs him.
"Ugh, more or less."
Thor puts a heavy hand on Tony's shoulder. "So. I thought you were dead."
"Yeah. Turns out death isn't that peaceful."
"It only is when its time has truly come."
"What?"
"Something Loki taught me. Come, I'll give you a glimpse of your legacy."
"No one knows who I am, apparently."
"But your impact lives. It's okay, you know, no one remembers the name of the shortest-reigning Asgard king in history. Valkyrie totally eclipsed me."
So anyway, Thor shows Tony around. That night Tony sleeps at the hotel under the name of Howard Potts. Can't fall asleep. Remembers his conversation with Thor at dinner.
"How did they live?", Tony asked in the middle of a silence.
Thor dropped his fork, had a little smile, knowing what Tony meant. "Long", he replied.
"Happily?"
Thor sighed. Tony looked down.
So he gets up and takes a car, I don't really care whose, let's assume they borrowed a car during the day. Arrives some time later at the lake house. It's empty and dark, doesn't look inhabited. As he gets out of the car, memories fill the place like ghosts. He sees the happy times of Pepper, Morgan and him, until his own memory slowly disappears and three becomes two and the happy place becomes this dark and empty place again.
In the sanctum, where the stone the kids found is now hidden, the stone glows brighter and brighter. From outside, the sanctum trembles.
Thor finds Tony in the lab. It's dawn.
"Been working, huh?"
"Yeah. The mind's busy. There's still a lot of things I can use in here. Anyone else lived here after us?"
"Yeah. Parkers."
Tony raises an eyebrow, then chuckles. And goes back to whatever he's fixing on his workbench.
"You're planning on going back, are you?", Thor asks.
"I don't belong here."
"There might... Be one thing we need your help with before."
They're at the sanctum. There's a big hole in the roof, like when Hulk fell from the sky.
"We suspect whatever was there came out of that stone you came out of yesterday. Any idea what it could be?"
"Yeah. It's a chitauri."
The sorcerer squints. "The chitauris have been extinct for two thousand years."
"Well I guess I've been running away from them for two thousand years."
It's Thor's turn to squint. "When you said death wasn't peaceful..."
Tony paces the room, sits on the armchair in a corner. "When I snapped and died... I found myself in this world. I supposed that was the afterlife. Except I took everyone else with me. All those who were snapped and me, we didn't really die. And even when we died in that world, we... Couldn't die. I fought at first and when I realized that, I hid. And planned my way out. Looks like they found my way out."
"The stone."
"Yeah. I guess it would've never worked had no one found it to activate it on the other side."
We see the arc reactor floating down the water after Pepper slips it on the lake at the funeral, floating further and further away until it sinks to the bottom of the lake and rolls down slowly, passing the various weathers and passing time, disintegrating slowly, forming a smaller round shape, until someday that small round shape glows again, still travelling for some time until finally, a kid picks it up, drawn by this underwater glow.
"Tony. You created an infinity stone. A ressurection stone." Thor looks more proud than surprised.
"I created a portal. And I didn't close it."
Thor snorts. "Yeah, it's just chitauris, this should be solved in a minute."
There's a crack sound and a blinding light. Loud steps are heard. Tony breathes loudly.
"I told you I'd always find you, Stark."
There's shrieks and other deafening sounds around there, coming in louder and quicker like a flood. There's a lightning and Tony's projected backwards as the sanctum blows up. Among the flames, Thanos. In the grey smoke around him, his alien army.
"How interesting does the game become when it's real", Thanos says, walking forward slowly. "How should I kill you this time? Crush your skull against the wall? Tear your heart out of your body again? Cut your head off?"
"The only head off will be yours", Thor says, throwing stormbreaker. "Run!"
Tony runs, but towards the sanctum as Thor fights Thanos one on one. There, he looks for a weapon and finds a sword. Just as he takes it from the wall, something arrives behind him and Tony blocks the alien's pointy arm with his sword. Tony's become good at sword fighting just because I love sword fights and I want to see sword fights in superhero movies. So Tony's become good at it because he's got two milleniums of self training.
Anyway then Thor and Tony meet again, fight side by side, and then there's more noise coming, people in superhero suits appear, and lights in the smoky sky - iron armours.
"What's this?", Tony asks.
"Your legacy", Thor says with a proud smile.
Carol, Valkyrie and Nebula show up too. Loki too, as a frost giant because I'm mad we didn't see that in Endgame. There's webs being cast around Tony to protect him, a captain America shield being thrown, etc etc.
Tony keeps looking for something in the sanctum, still sword fighting the villains who come in his way, until he finds it again, the arc reactor stone, and he holds it in his fist, squeezing tightly. "Come on, please work". The walls collapse around him and in front of him, revealing Thanos behind it. Thanos smiles and with rapidity, throws a dagger at Tony, that hits his heart just as the nanosuit finishes wrapping itself around his body. The dagger falls to the ground. And Tony rises.
"Well hello, Mr Stark", a voice says in his helmet.
"Who are you?"
"A Stark."
Anyway, the fight ends with Nebula killing Thanos as it should be.
Once the fight is over, everyone is on the ground. Every iron people nanotech their suit away, I don't know how to say that. There's a hell lot of them. "So which one of you is a Stark?", Tony asks.
Several of them raise their hands, then step to the front. Among them, there's Riri Williams. Well that's up to you, I don't know much about her but I liked the idea that she could have very old Starks ancestors. Oh oh, or maybe she could have Rhodes ancestors! Maybe a Rhodes and a Stark at some point got more than friends. And then the daughter married a Williams, really whatever you want.
"The Iron Army is one of the most famous and respected in the universe", Thor explains.
The kids at the beginning just didn't really know about it because Earth has been one of the most peaceful planets in a long time.
Also there's a spider kid who introduces himself as a Parker and he looks exactly like Peter. Or he looks like the Peter Parker from into the spider-verse, that could be fun. Up to you.
Anyway. After that Tony manages to build the time travel stuff again and Thor helps him go back in time. "Have a happy life, Tony".
Tony arrives in 2023 right after his funeral. Everyone's gone. Tony knocks at the door. They reunite properly, with tears of happiness and kisses and then Tony says, holding them in his arms, "we're gonna live long. And happily." The end, I have no idea what I just wrote and I'm sorry for the plot holes, I definitely got carried away.