Well, he might start his own secret training. Away from Hogwarts, he could find a hidden place and train with some unknown but powerful wizards. This new training could give him different skills and powers that Hogwarts couldn't offer.
Another way the plot could develop is that Harry's rejection of Hogwarts causes a rift in the wizarding world. Some support his decision, seeing it as a brave step towards change, while others condemn him. This leads to a power struggle between different factions. Harry then has to navigate through this complex political situation, trying to prove that his way is better while also facing the challenges of being an outcast from the traditional Hogwarts - centered wizarding society.
In some fanfictions, Harry's disappearance could lead to the discovery of new magical powers or places. Maybe he stumbles upon a hidden magical realm while in hiding. This new place could have its own set of rules and powers. As he tries to figure out how to get back to Hogwarts or deal with the situation that made him disappear in the first place, he has to learn about these new powers and make alliances with the beings in this new realm.
Well, it could lead to Harry feeling a bit heartbroken at first. But then he might focus more on his fight against the dark forces. He realizes that their friendship is more important than a romantic relationship that wasn't meant to be.
As the plot progresses, Harry might start to realize the true extent of what he's gotten himself into. He could face internal struggles, doubting his decision. Maybe he'll discover some secrets about the Goblet or the tournament that he wasn't supposed to know. This could lead to a whole new set of challenges and adventures, like having to deal with dark magic associated with the tournament that was hidden from the public.
After Umbridge uses Veritaserum on Harry in a fanfic, the plot could develop in various ways. If Harry reveals secrets about the resistance against Umbridge, she could crush it. On the other hand, his friends might try to rescue him from the situation and that could start a whole new adventure of escaping Umbridge's clutches.
Well, it might show Harry on a journey of self - reliance. He could be traveling alone, facing new challenges outside of the school's protective bubble. Maybe he meets new allies who help him understand the bigger picture of the magical world that Hogwarts had shielded him from.
The plot might develop with Harry exploring the non - Hogwarts magical world. He could meet new characters who introduce him to different magical cultures and spells.
In some fanfictions, they might have a bit of a rough start. Maybe Harry has some post - war trauma that makes it difficult for him to fully open up at first. But Ginny, being strong - willed, helps him through it and their relationship deepens as a result. They learn more about each other's dreams and fears outside of the Hogwarts environment. They could start to realize that they want to be more than just boyfriend and girlfriend, but true life partners in all aspects of the wizarding world.
Often, his friends would rush to his aid. They might try to find a cure or figure out what's wrong with him. Maybe Hermione would start researching in the library right away.
Often, it starts with the incident that causes the concussion. Then it shows how Harry's daily life is disrupted. For example, he may struggle in his classes or have difficulty with his Quidditch training.