Tony could have a very complex reaction. He might be a mix of angry, sad, and confused. He may feel like he's lost control of his life, which is something he hates. He could also be worried about Pepper and the baby, even if he's angry at her for leaving. He might start to make changes in his life, trying to become a better person in the hopes that Pepper will come back to him. He may also feel a sense of guilt, thinking that his actions led to Pepper leaving and her having to face the pregnancy alone.
At first, Tony might be in denial. He's so used to having Pepper by his side that he can't fathom her leaving, especially when she's pregnant. As time goes on, he could become very sad and start to reflect on what he did wrong in their relationship. He might try to win her back, using his resources and intelligence to show her that he can be a good partner and father.
On the other hand, some fans might be interested in seeing how the author develops the story from such a controversial starting point. They could be curious about how Pepper will respond and if there's a chance for redemption for Tony.
Well, perhaps Pepper realizes she and Tony have grown apart in some way. Maybe she feels neglected due to Tony's constant focus on his work or superhero duties. As for being pregnant, it could be that she discovers she's pregnant just as she decides to leave, adding a whole new layer of complexity to the situation. She might leave to protect the baby from the dangerous world that surrounds Tony.
The fanfiction might explore how the child copes with this situation too. Is the child aware of the reasons? Does the child try to reunite the parents? There are so many possible storylines that can branch out from this one simple premise of Pepper leaving Tony with a child.
In this fanfiction, Pepper might struggle a bit with the idea of being pregnant while Tony is constantly in the spotlight as Iron Man. She could worry about how their child will grow up in such a public environment. However, Tony reassures her that they can create a normal family life within their extraordinary circumstances.
If Pepper leaves Tony in the fanfiction, it could disrupt the Avengers' dynamic. Tony might become more withdrawn and less focused on the team, which could affect their mission planning. For example, he might not be as quick to come up with technological solutions during battles.
Maybe in the fanfiction, Pepper leaves Tony after a big argument about his recklessness. He's always putting himself in danger, and she can't take it anymore. She leaves to find herself and pursue her own career goals that she had put on hold for him. Tony then has to learn to be more responsible and make some changes in his life if he wants her back.
Maybe in the fanfiction, Tony leaves Pepper due to his own self - doubts. He might think that he is not good enough for her, perhaps because of his playboy past or his superhero lifestyle which often brings chaos and destruction. So he chooses to leave to spare her from his 'imperfections'.
Obviously, the main characters are Tony and Pepper. Tony is a complex character, a genius inventor and superhero. Pepper is his love interest and also a very capable businesswoman who often has to deal with the consequences of Tony's actions.
In fanfiction, perhaps Tony would use his genius to create a special prenatal care system for Pepper. It could be something that uses his Iron Man technology to ensure the healthiest pregnancy possible. He might even be able to detect any potential problems long before traditional medical methods.
In these fanfictions, their relationship is explored through the shared responsibilities. Tony might take on more domestic tasks like making sure Pepper has a healthy diet. They also communicate more deeply. They discuss their hopes and fears for the child. This could lead to them resolving some past issues in their relationship. For instance, if there were any trust issues before, the pregnancy could be a time to rebuild that trust.