It could be that a new threat emerges. Maybe another android, stronger than Cell, was observing the fight and decides to take advantage of the chaos after Gohan's death. This new android could become the main antagonist as it poses a greater danger to the remaining fighters.
Perhaps Gohan's own overconfidence could lead to his death. He might underestimate an enemy's power or a dangerous situation and make a wrong move that results in his end. For example, he could rush into a fight without proper preparation thinking he can handle it easily.
In such a fanfiction, perhaps future Gohan could warn present - day Gohan about upcoming threats that he has faced in his own timeline. He might share his experiences and knowledge, which could make present Gohan a stronger fighter and a wiser person.
Another scenario could be that Gohan contracts a deadly and incurable disease in the fanfiction world. Despite the efforts of his family and friends, including the use of any available advanced technology or magic, he succumbs to the illness, leaving everyone in mourning.
A possible plot twist could be that future Gohan is actually an impostor sent by an enemy to manipulate the real Gohan. Another twist might be that when they meet, their powers combine in an unexpected way that causes some sort of time rift or a change in the timeline.
Future Gohan's character development would likely involve him becoming more resolute and determined. After all the hardships he's faced, he would grow stronger both physically and mentally. He might start as a somewhat broken hero, but as the story progresses, he'd regain his confidence and find new purpose in protecting what's left of his world.
In a fanfiction where Future Gohan meets Goku, it could be an emotional reunion. Gohan might be filled with a sense of relief and joy, seeing his father again. He could show Goku all the things he's been through in the future, and Goku would be both proud and sad about what his son has endured.
Perhaps Gohan sacrifices himself to save the other Z - fighters. He might choose to take on Cell's full - power attack that was meant for all of them, and in the process, he loses his life. In the fanfiction, it could also be that Cell has some sort of hidden power - up that catches Gohan off - guard and leads to his death.
In this fanfiction, if Gohan dies in the Cell Games, perhaps the story could focus on how the other characters cope with the loss. For example, Chi - Chi could become a more hardened character, vowing revenge on Cell or any other threats. Piccolo might take on a more fatherly role to Goten, trying to train him to be as strong as Gohan was. And the Earth might be in a state of mourning, which could attract new villains who see it as a time of weakness.