A plotline could be that the Avengers, in their grief over Tony's death, try to reverse time not just to stop Thanos but specifically to save Tony. They manage to find a way to go back further in time than they originally did and prevent Tony from getting into the situation where he has to sacrifice himself. This could involve teaming up with past versions of themselves and other characters they haven't interacted with before, all while trying to keep the timeline from collapsing.
One possible plotline could be that Tony Stark uses his genius to find an alternative way to defeat Thanos without sacrificing himself. Maybe he discovers a new element or technology during the final battle that turns the tide. Another plotline could involve time travel having unforeseen consequences that bring Tony back to life in a different timeline, and he has to find his way back to his original one.
In some fanfictions, Tony Stark might survive because of the intervention of other powerful beings. For example, Doctor Strange could have seen a different future where Tony lives and uses his magic to ensure that outcome. Or perhaps the Soul Stone has some hidden power that can revive Tony after he snaps his fingers. It could also be that Tony had a backup plan all along, like uploading his consciousness into an AI before the final battle, so he can still be around in a different form.
Morgan Stark, Tony's daughter, could be a central character. Her existence might be what drives the other characters to find a way to bring Tony back. Rhodey, as Tony's long - time friend, would surely be involved in any attempt to save him. And there could also be appearances from characters like Nick Fury, who has a knack for getting involved in important events and might offer some resources or knowledge to help Tony survive.
One way could be through some kind of time - related magic. Maybe Doctor Strange finds a way to manipulate time even more precisely than he did in the movie. He could create a special time loop that spares Tony's life while still achieving victory over Thanos. Another possibility is that Pepper, using her own intellect and some Stark technology she's been secretly working on, manages to reverse the effects of the Infinity Stones on Tony at the last moment.
A common plot involves Tony being resurrected by some kind of magic or advanced technology. For example, the Wakandans could have a secret method of bringing the dead back to life that they use on Tony. Or, in the Quantum Realm, there could be a phenomenon that reverses death, and Scott Lang discovers it and uses it to save Tony. Also, some fanfictions have Tony's soul being saved by a powerful being like the Sorcerer Supreme and then being put back into his body.
A plotline could involve Tony Stark joining Hydra to spy on them for the Avengers. He pretends to be on their side, but secretly feeds information back to his old team. Along the way, he has to be careful not to get caught and also has to deal with Hydra members who start to suspect him. This would create a lot of suspense and action in the fanfiction. Also, there could be a plot where Tony tries to change Hydra's ideology from within, using his charm and intelligence, but it turns out to be a much harder task than he thought.
Perhaps there's a power struggle over a new technology or a powerful artifact. Tony wants to use it for what he believes is the greater good, but Steve opposes him. Their clash escalates to a point where Tony, in a fit of rage or desperation, kills Steve. Or maybe it's a situation where Steve discovers some dark secret about Tony's business dealings and Tony kills him to keep it quiet.
One possible plotline could be that Tony Stark sees a future where his technology is misused and he has to find a way to prevent it. For example, he might see his Iron Man suits being used for evil purposes by a powerful villain. Another could be that he sees a future without him, and realizes the importance of training a successor, like Peter Parker, more seriously. Or he could see a future where the Avengers are disbanded due to internal conflicts, and he tries to mend the relationships in the present to avoid that future.
One possible plotline could be that a powerful magical spell in the Harry Potter universe somehow crosses over and affects Tony Stark, causing the mpreg situation. Then, the story could revolve around Tony trying to figure out what happened and how to reverse it, with Harry Potter characters helping or hindering him. Another plotline might be that a new form of technology in Tony Stark's world has an unexpected side effect when combined with the magic of Harry Potter's world, leading to the mpreg. And the characters have to find a way to deal with the social and magical/technological implications.
A possible plotline could be them having to keep their marriage a secret from the world. Maybe because of Tony's business rivals or Natasha's undercover work. They would have to navigate their relationship while hiding it from everyone, which could lead to some really tense and exciting moments.
One possible plotline could be that Tony Stark discovers a new technology that allows him to have wings. He could use these wings to enhance his superhero capabilities, like flying faster and more stealthily than with his regular Iron Man suit. Maybe he uses the wings to access hard - to - reach places during a rescue mission or to surprise his enemies from above.
A simple plotline could be that Tony Stark, being the genius he is, discovers a way to enter the wizarding world. He meets Harry Potter and they exchange knowledge. Tony shows Harry some of his high - tech gadgets like the Iron Man suit, and Harry shows Tony some basic spells. They then team up to fight a new threat that emerges in the wizarding world that requires both magic and technology to defeat.