There's a chance that Sirius Black could rescue Harry. Even though he was in prison for a long time, if he somehow escaped or was proven innocent early in this fanfiction scenario, he would be eager to take care of Harry. Sirius was Harry's godfather after all. He could give Harry a family environment full of love and support, and also teach Harry about his parents from a more personal perspective. Harry would also learn a lot about the Marauders from Sirius.
Dumbledore could rescue Harry. He's always been watching over Harry and would surely sense if the Dursleys had abandoned him. Dumbledore has the power and wisdom to take Harry to a safe place, perhaps a different magical family or a special hideout. He could also start teaching Harry about his past and his parents earlier, which would give Harry a better understanding of his place in the wizarding world.
Well, he might be found by someone unexpected. Maybe a group of young witches and wizards who are on an adventure outside of Hogwarts. They could take Harry under their wing and introduce him to the wizarding world in a completely different way. Instead of the strict rules and regulations that he later faces at Hogwarts, he could learn magic in a more free - spirited and experimental environment. This could shape his character to be more rebellious and independent, not afraid to break the rules when he believes they are unjust.
Harry might rely on his own wits and magic. Since he has some natural magical abilities, he could use them to fend for himself, like conjuring food or finding shelter.
Hermione could be one to rescue Harry. She might have discovered some new spell or potion that allows her to bypass the protections around the Dursleys' house and get to Harry. Then she'd use her intelligence and quick thinking to get him out of there safely.
In some fanfictions, Neville could play a crucial role in rescuing Harry. Neville has grown a lot throughout the series and could surprise everyone with his courage and newfound magical abilities. There could also be some unexpected allies, like a group of centaurs or house - elves who decide to help because they recognize the importance of Harry in the fight against Voldemort. House - elves, for example, are known for their powerful magic that is often underestimated, and they could use it to their advantage to free Harry.
Well, in some versions of the 'Dursleys abandon Harry fanfiction', they abandon him due to social pressure. They are worried about what their neighbors or friends might think if they find out about Harry's true identity. Also, Petunia may have some deep - seated jealousy towards her sister Lily for being a witch, and this negative feeling extends to Harry, leading them to abandon him.
His Hogwarts friends could be his allies. Ron and Hermione might come up with a clever plan to get Harry out. They could use the Weasley's magic - enhanced car to fly to Privet Drive and then create a diversion while Harry sneaks out. Another ally could be Hagrid. He has a soft spot for Harry and might show up with a large magical creature, like a friendly hippogriff, that Harry can ride away on.
Hermione could be the rescuer. Maybe she discovers through her research that Harry is in a bad situation at the Dursleys' and decides to take action. She uses her intelligence and magic skills to break into the Dursleys' house and get Harry out. Then they would go on an adventure together, and Hermione would be like a mentor to Harry in a way, teaching him things she has learned from books.
Hedwig could be a potential ally. She could carry messages to Harry's friends at Hogwarts, alerting them of his situation. Even though she is just an owl, she has shown loyalty and intelligence in the original series.
One way the Dursleys can be good in fanfiction is if they are forced to face the consequences of their actions early on. For instance, they might receive a warning from the wizarding world that if they don't treat Harry well, there will be serious repercussions. So they start to be nicer to him. They could provide him with a proper room, better food, and allow him to have friends over.
In some Harry Potter fanfictions, the Dursleys are depicted as nice. This could be a really interesting take. It might show how they could have been different if they hadn't been so influenced by their dislike for magic. Maybe they could have supported Harry more, or at least been less cruel. For example, a fanfiction could explore a scenario where Vernon Dursleys actually encourages Harry's academic achievements at school, instead of always putting him down.