One possible plotline is that Tony's heart attack forces the Avengers to take a step back from the Civil War. They might start to question the purpose of their fighting when one of their own is in such a critical state.
A fanfiction with Tony Stark having a heart attack during Civil War can open up numerous storylines. It could show the reactions of other characters like Pepper Potts, who would be extremely worried. His fellow Avengers might put aside their differences temporarily to ensure his survival. Also, it could lead to a deeper exploration of Tony's health issues that were perhaps overlooked before the heart attack, and how it affects his future decisions in the ongoing conflict.
One possible plotline could be Tony Stark's struggle to continue being Iron Man after the heart attack. He might have to rely more on his intellect and less on his physical strength, leading to some really creative solutions in his battles. Another could be his friends and teammates rallying around him to support his recovery, which would show the strong bonds in the Marvel universe.
One plotline could be Peter struggling with choosing between Tony's side and his own moral compass. Maybe he tries to find a middle ground to keep his relationship with Tony intact while also doing what he believes is right.
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.
One possible scenario in this fanfiction could be that a de - aged Tony Stark brings a new perspective to the events of Civil War. He might be less jaded and more idealistic, trying to find solutions that the older, more conflicted Stark couldn't see. Maybe he forms unexpected alliances with other characters based on his fresh outlook.
One consequence could be that the Avengers are left in disarray. Tony was a key figure in terms of resources and technology. His death might mean a lack of funding and advanced equipment for the team.
In this fanfiction, Tony Stark having a heart attack might force him to reevaluate his life. He might start thinking about all the times he's put himself in danger without much regard for his own well - being. It could also be a turning point for his relationships, like with Pepper Potts. She would be extremely worried and might take more control over his lifestyle to prevent further health issues.
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.
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 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.