Their relationship could have become stronger. After Loki's 'death' in the movie, Thor was devastated. If Loki survived, Thor would likely be more protective of him. They might start to trust each other more fully, putting aside their past differences.
If Loki survived Infinity War in fanfiction, their relationship could have evolved into a more equal partnership. Loki has always been in Thor's shadow, but now they could be seen as equals. They would both bring different skills to the table. Thor with his brute strength and Loki with his cunning. This new dynamic would change how they interact with each other and the other characters in the Avengers.
In some fanfiction, it shows a more reconciled relationship between Loki and Thor in Infinity War. Instead of the conflicted and somewhat hostile relationship in the movie, they are shown to be more understanding of each other. Loki might be more open about his fears and Thor more accepting of his brother's past actions.
One way to 'fix' the situation in a fanfiction could be to have Loki's faked death in Thor: The Dark World be more thoroughly investigated by Thor. If Thor had been more suspicious and dug deeper, he might have uncovered Loki's real plan earlier. This could have led to them working together more effectively against Thanos in Infinity War, preventing some of the tragedies that occurred.
In a fix - it fanfiction, Thor and Loki could start by having an honest conversation. Loki could reveal his true intentions and fears to Thor. This newfound honesty could strengthen their bond and make them a more effective team against Thanos. Instead of the constant mistrust between them, they would be united and support each other throughout Infinity War.
If Loki survived in Infinity War fanfiction, it could have led to a very different outcome. He might have used his trickery to deceive Thanos in some way. Maybe he could have pretended to be on Thanos' side while actually working against him. This would have added an extra layer of intrigue to the story as the other characters would have been unsure of his true motives.
If Thor died in Infinity War in a fanfic, Hulk's role might have become more prominent. Since Thor was one of the few who could somewhat control Hulk, his death could lead to Hulk being more unruly or having to find a new way to be useful. Also, Thor's death could have made Thanos seem even more invincible. This could have led to some characters losing hope earlier. For instance, Black Widow might have become more desperate and made different decisions. And Thor's death could have changed the power dynamics in Asgard, which might have had implications for the overall cosmic balance in the MCU.
When Thor is mean to Loki in fanfiction, it can lead to a downward spiral in their relationship. Loki, feeling constantly attacked, may lash out in more extreme ways. Thor, on the other hand, may double down on his meanness, believing it's the only way to deal with Loki. This can create a cycle of animosity where any love or brotherly bond they had is overshadowed by anger and distrust. For example, Loki could start to form alliances with Thor's enemies out of spite, and Thor would see this as confirmation of Loki's untrustworthiness, making the relationship even worse.
Loki's relationship with Thor would be filled with mixed emotions. He could be resentful at first for getting into this situation, but as time goes on, he might come to rely on Thor more. They would have to communicate more openly about their feelings and fears, which could strengthen their bond in a different way than before.
In fanfiction, Loki and Thor could have formed an alliance with other unexpected characters during Infinity War. Maybe they would team up with the Guardians of the Galaxy in a different way. Loki could have used his knowledge of the cosmos and his ability to blend in to gather more information about Thanos' plans. Thor could have shared his Asgardian battle strategies with Star - Lord and the others. This would have led to a completely different dynamic in the fight against Thanos, perhaps even resulting in a victory that didn't happen in the movie.
It could strengthen their bond. They now have a common responsibility to protect and guide their younger brother. For instance, Thor might take on a more fatherly role, teaching him about honor and courage, while Loki could teach him some of his sly ways to outwit enemies, but also warn him of the dangers of excessive trickery. Their relationship could become more complex as they balance their own differences while raising the younger brother.
Their interaction could also lead to a change in their relationship dynamic. In Asgard, Thor was often the more dominant and 'good' brother, while Loki was the troublemaker. In the TVA, they could become more equal. Loki might have knowledge about the TVA that Thor doesn't, and Thor could bring his strength and loyalty to the table. This new dynamic could be a turning point for both of their characters as they navigate the strange world of the TVA together.