In a 'Percy Jackson leaves earth' fanfic, he might end up in a whole new realm of gods and monsters. Maybe he discovers a parallel universe where the rules of the Greek gods are different. He could encounter new versions of his friends or enemies and have to learn new powers to survive.
He might meet other inter - galactic beings. For example, some sort of space - faring demigods from a far - off galaxy. Or he could encounter powerful entities that are the rulers of other planets.
Perhaps he'll meet other demigods who have also left Earth for various reasons. They could form a new group and face new challenges together. For example, they might have to deal with a powerful alien being who wants to use their demigod powers for its own evil purposes. Percy would then need to use his wits and strength to lead the group and find a way to defeat this new enemy.
He might go on a solo adventure to discover more about his powers. He could encounter new mythical creatures that he hadn't seen around the camp. Maybe he'll meet some other demigods who are on the run or have their own secret quests.
He could go to the Underworld of another planet, if such a place exists in the universe he lands in. It might be filled with different kinds of dead souls and ruled by a different kind of Hades - like figure.
Well, if Percy Jackson becomes the god of earth in fanfiction, it would be a huge change. He'd likely gain the ability to manipulate all aspects of the earth, from the soil to the highest mountains. His relationship with other gods would shift too. He might become a more powerful figure, which could lead to some jealousy among the other gods. Maybe he'd start to reform the way the gods interact with mortals, using his own experiences as a demigod to create a fairer system. And he could use his powers to discover new, hidden parts of the earth, full of magic and mystery.
Percy might be very confused at first. He would wonder why his mother, who has always been there for him, suddenly left. He could start to question if he did something wrong. In some fanfics, he may go into a state of denial, not wanting to believe that she's really gone.
Another reason might be that she is forced to leave. There could be a magical or divine force at play. Maybe a god or goddess, who has some grudge against Percy or his father Poseidon, manipulates the situation so that Sally has no choice but to abandon Percy. This would add a lot of drama and conflict to the fanfic.
Well, some gods might be amused. If Poseidon read fanfic about his son Percy, he might chuckle at the creative interpretations of Percy's adventures. But others, like Ares, might be angry if the fanfic portrayed him in a way he didn't like. He could even try to take revenge on the writer, thinking it was an insult to his godly status.
They might be amused. The gods in the Percy Jackson universe have a sense of humor. Reading fanfic could give them a new perspective on how mortals view them and their world.
In a fanfic scenario where Percy Jackson joins Kronos, it could be a very interesting exploration of the 'what - ifs'. Percy has a strong sense of justice, so for him to side with Kronos, Kronos must have presented a very convincing argument. It could be that Kronos showed Percy a future where the demigods are constantly oppressed by the Olympians. However, this would also mean Percy has to go against his instincts and the relationships he has built. His friends like Annabeth would be in shock and try to bring him back to the right side. This could lead to some intense battles not only between the demigods and Kronos' forces but also within Percy himself as he struggles with his new allegiance.