Yes. In 'Infinity War', Thor has a significant role. His journey to get a new weapon to face Thanos is crucial. Thanos, on the other hand, is the main villain driving the plot forward as he tries to collect all the Infinity Stones. Their fates are intertwined throughout the movie.
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 some comic iterations of Infinity War, Thor tragically meets his end. However, comic storylines can vary, and there might be alternate universes or continuities where he survives.
Thor is on a mission to stop Thanos. Thanos is on a mission to get all the Infinity Stones. Their goals are in direct opposition, making the movie revolve around them.
In this kind of fanfic scenario, the entire plot of the MCU could have been drastically different. For example, the remaining Avengers would have lost one of their most powerful members. Thor's strength and his ability to wield Stormbreaker were crucial in the actual Infinity War. Without him, the battle against Thanos on Wakanda might have been a total disaster much sooner. His death could have also deeply affected the morale of the other heroes, perhaps leading to different alliances and strategies that we didn't see in the original storyline.
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.
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.
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.
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.