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.
There were a few novels that could be recommended, including Those Years Living in the Future World of Dragon Ball, If Dragon Ball, Latiz took Gohan away, and The Strongest Sun Gohan of Dragon Ball. These novels all used Gohan as the protagonist, telling his growth and adventures in the Dragon Ball world. These novels might satisfy your need for Gohan to be the protagonist.
His father, Goku, would be deeply affected. He might feel guilty for not being there to protect Gohan or for not training him better. Vegeta, too, would be shocked. Despite their rivalry, he respects Gohan's power. His death could make Vegeta more determined to defeat their enemies. And Chi - Chi would be heartbroken. She had always hoped for Gohan to have a normal life, and his death would be a cruel blow.
In this fanfiction, Gohan might learn valuable life lessons from Grandpa Gohan. Maybe Grandpa Gohan would teach Gohan some old - fashioned martial arts techniques that have been forgotten over time.
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.
Piccolo might also be a savior. He has a soft spot for Gohan since they trained together. He could use his strategic mind and powerful attacks to outwit Raditz and rescue Gohan. Maybe he teams up with Goku for an even more epic rescue mission.
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.
Naruto would probably be the most interested. He loves making new friends and Gohan's power would surely catch his attention. He'd be eager to learn about Gohan's world and his abilities.
It could be a new, unknown enemy. Maybe someone from a far - off planet who has a grudge against the Saiyans. This character could be really powerful and sees Gohan as an easy target at first, so he throws a punch.