In fanfiction, if Ash were to die in Pokemon XYZ, it would be a huge shock to the Pokemon world. His friends like Pikachu would be devastated. Maybe Team Rocket would even feel a strange sense of loss. It could lead to a whole new storyline where his friends try to avenge his death or carry on his legacy of becoming a Pokemon Master.
He could die in a battle against a very powerful and evil Pokemon. Maybe a new, extremely strong legendary Pokemon that he underestimated, and it managed to land a fatal blow.
The unique thing about Pokemon XYZ abridged fanfiction is that it often takes the existing story and condenses it while adding new elements. For example, it might focus more on the relationships between the characters.
Team Rocket could also be the focus of a reunion fanfiction. Maybe they've reformed and are having a reunion to celebrate their new lives away from their villainous ways. They could be showing off their new Pokemon or skills that they've developed.
Obviously, Dark Ash is one of the main characters. He's the center of the story with his transformed state. Serena might also be a main character as she could be trying to reach out to Ash or deal with the new Dark Ash.
The main appeal is their relationship. In the series, they have a special bond. Fanfictions allow fans to explore this bond further, whether it's romantically or as great friends. It gives a chance to see them in new situations not shown in the original series.
One great fanfiction could be 'Ash and Serena's Unseen Adventure'. It might explore their relationship further as they journey through a new region filled with unique Pokemon. Another could be 'Serena's Dream Come True with Ash', where Serena finally achieves her long - held dreams while Ash is right by her side supporting her. And there's also 'The Bond of Ash and Serena', which delves deep into how their bond grew over their adventures.
One idea could be that the main characters reunite during a big Pokemon tournament. They each have new Pokemon and strategies, and they compete against each other in an epic battle. It could also be a reunion during a crisis, like a natural disaster in the Pokemon world, and they have to work together to save Pokemon and people.