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.
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.
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.
In Infinity War fanfiction, Loki can be alive. Fanfic authors have the creative liberty to rewrite the events. They might bring Loki back to life using magic or some other means. For example, Loki could have faked his death and gone into hiding, only to reappear later in the story to help the heroes fight against Thanos. His survival can add an interesting twist to the story and create new interactions between characters.
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.
Another aspect could be Loki's relationship with the other characters. Without Thor, he would need to build new alliances. He could form an unexpected bond with Hulk, perhaps using Hulk's brute strength and his own cunning to create a unique duo. They could then set out on a mission to retrieve the Infinity Stones from Thanos, with Loki devising elaborate plans and Hulk providing the muscle.
If Loki survived Infinity War, it might have opened up new storylines and character developments. He could have played a crucial role in finding a way to reverse the damage or caused more chaos.
Loki could gain the ability to harness Thor's lightning. Maybe in the moment of Thor's death, some of his power transfers to Loki. This would be a huge boost to Loki's combat abilities and could make him a more formidable opponent against the likes of Thanos.