One possibility is that Tony could prevent some of the major disasters that occurred in the Marvel Universe. For example, he might stop Loki from getting the Tesseract in the first Avengers movie. This would change the entire timeline and prevent the destruction of New York City that followed. Another thing is that he could meet his parents at a different time, which would be an extremely emotional encounter for him. He might also be able to use his advanced knowledge to help Howard Stark with some of his early inventions, potentially accelerating the technological progress of that era.
His character could become more humble. Going back in time and seeing the past versions of people and events might make him realize how much he has changed over the years. He may also become more cautious. Knowing the consequences of certain actions from his original timeline, he'll be more careful with his decisions in the past. For example, he might think twice before revealing his identity as Iron Man too soon.
In fanfiction, anything can be possible. Morgan Stark bringing Tony Stark back could be achieved through various means. Maybe she discovers some advanced technology her father left behind that has the power to reverse time or bring someone back from the dead in a scientific way. It could also be something more magical or otherworldly if the fanfic takes a more fantastical turn.
She might change the course of events in the past. For example, she could prevent some tragedies that happened to her family. Maybe she would use her advanced knowledge to help her father, Tony Stark, earlier in his life, which could potentially lead to a different future for the Avengers and the whole world.
Well, in this fanfiction, Stark could start by being in awe of Wakanda's beautiful landscapes and hidden - away - from - the - world nature. He'd then meet the Wakandan heroes like Black Panther. Their different approaches to heroism and technology could clash at first. Tony, with his brash and open - source style of tech, might not understand Wakanda's more secretive ways. But as the story progresses, they could find common ground in protecting the world from bigger threats. Maybe they'd team up to face a new enemy that neither could defeat alone, combining Stark's high - tech suits and Wakanda's vibranium - powered weapons.
Well, a cool plot in an Arya Stark goes back in time fanfiction could be that she travels back to the time when the White Walkers first started to become a threat. Arya, with her knowledge of the future, could try to find a way to stop them from ever becoming such a powerful force. Maybe she'd team up with some of the early Night's Watch members in a way that changes the entire history of the war against the dead. Also, she could go back to the time when the Starks were still in a more powerful position in the Seven Kingdoms and use her skills to strengthen their alliances.
Sansa would be more assertive in her political moves. She has seen the consequences of inaction and bad decisions in the future. So, she would be quicker to make decisions that benefit her family and herself. For example, she might be more involved in military strategies to protect the North.
One idea could be that Sansa goes back in time and tries to prevent the Red Wedding. She could use her knowledge of the future to warn her family and change the course of that tragic event.
The plot could start with Morgan growing up and feeling the absence of her father deeply. She might stumble upon some hidden files or a secret project of Tony's that gives her an idea on how to bring him back. Then she embarks on a dangerous and challenging adventure to gather the necessary resources and knowledge.