Well, it would change a lot. Harry would grow up without his father's influence, which could make him even more of an outcast in the Dursley household. Without James' presence in his life, Harry might not have the same sense of self - worth that he got from knowing his father was a brave Gryffindor. Also, the relationship between Harry and his mother Lily would be very different. Since she made James forget Harry, there must be some underlying reasons that could affect how Harry views his mother.
Harry would be heartbroken. He'd likely first try to jog their memories in simple ways, like showing them things that were important to their family. He might be in denial at first, thinking it's just a temporary thing.
One possibility could be that Lily uses some kind of magic, perhaps a very powerful and rare spell. Maybe she does it out of a sense of protecting James from the pain associated with Harry. In the fanfic, it could lead to a lot of confusion for James. He might start a new life without the knowledge of his son, and then as the story unfolds, there could be a series of events that slowly make him start to remember bits and pieces. For example, he might encounter people or objects that were related to Harry, which would trigger his subconscious.
Harry would likely be overjoyed at first. After all, he never really got to know his parents. Their return could give him a sense of family and belonging that he's always craved. It could also help him deal with some of his past traumas, having his parents there to support him.
They could be shocked at first. But then they might start to enjoy it as they see the creativity of the fans.
In such a fanfic, perhaps a villain manipulates time and alters the memories of James and Lily. They might be living in a different reality where Harry doesn't exist in their minds. Harry could then embark on a journey to find the source of this alteration and restore his parents' memories. He could encounter various allies and enemies along the way, all while trying to come to terms with his parents' current state.
It would shock many fans at first. Since in the original series, they are a loving couple. But some fans might be interested in seeing a different take on their relationship. It could also inspire more fanfics exploring different relationship dynamics within the Potter universe.
Harry's view of the world might change completely. He has seen so much darkness and death. With his parents' return, he could start to see the world in a more hopeful light. He may be more willing to forgive those who have wronged him in the past, like Snape. Their return would be a catalyst for a huge shift in his personality, making him more balanced and less haunted by his past traumas.
Well, they might be quite amused. They could be proud to see how much the fans love their son Harry. They might also be a bit surprised at some of the creative interpretations that fanfic writers come up with.
In the Stargate universe, Harry's magic would introduce an entirely new element. His spells for communication, like the Sonorus charm, could be adapted for long - distance communication between planets. His ability to transfigure objects could be used to create useful tools or even disguises when dealing with different alien races. This would give the Stargate teams an edge in their diplomatic and undercover operations. And his experience in fighting dark wizards could translate into strategies for fighting the various evil forces in the Stargate universe.
It would be very emotional. Harry, who has only known his parents through stories and memories, would now have the chance to actually build a relationship with them. They could be like mentors to him, guiding him in magic in ways he never had before.