In the manga, Goku does fall into hell as part of a complex and adventurous storyline. This event leads to many interesting developments and challenges for him.
Goku might run into past versions of his friends. He could see a younger Krillin or Bulma and have some really interesting interactions. He could also meet past versions of his enemies and try to change their fates. For instance, he could meet a young Vegeta and try to steer him away from the path of evil. This would be a huge change in the Saiyan's story.
There were novels where the main characters would go to hell and be reborn. These novels were often called the " Hell Rebirth Stream " or the " Dark Stream." The more famous ones included:
1 " Lord Snow Eagle ": The protagonist of the novel, Ye Fei, is an ordinary game player. However, he accidentally transmigrated to a world similar to a game. This world is ruled by an evil force, and Ye Fei's mission is to save this world. In the process of saving him, he encountered many difficulties and dangers. In the end, he became the leader of this world through constant fighting and hard work, and obtained the power of rebirth in hell after death.
The main character of this novel, Wei WuXian, is a Xianxia character who accidentally transmigrated to a world full of magic and monsters. In this world, he made many friends and enemies, and gradually grew up through constant adventures. In the final battle, he chose to go to hell to be reborn in order to save the world. After rebirth, he became an even stronger existence.
[3. Douluo Continent: The main character of this novel, Tang Wulin, is a soul master. He accidentally transmigrated into a soul master's world.] In this world, he had become a powerful soul master through constant cultivation and battle, and he had obtained the power of hell's rebirth after death.
The protagonists of these novels all experienced a lot of pain and setbacks, but after being reborn in hell, they became stronger and wiser beings to continue their mission.
Maybe Naruto goes to hell to rescue a friend or to face some powerful dark forces. For example, he might go to save Sasuke who got trapped there somehow.
In the fanfic, Goku could become friends with Naruto easily. Since they both have a strong sense of justice and a will to protect their friends. Goku might teach Naruto some of his training methods, like training under heavy gravity. And Naruto could show Goku the unique aspects of ninja villages and how they function.
One common theme is redemption. For example, they might face their past mistakes or the consequences of their actions in a more intense way in hell. Another theme is the power struggle. Since hell is often depicted as a place full of powerful and evil entities, Goku and Vegeta have to constantly prove their strength. Also, friendship and rivalry play a part. Their relationship is complex, and in these stories, they might have to rely on each other more than ever while still maintaining their competitive edge.
Vegeta would also be an important character. His rivalry with Goku would intensify even more. Seeing Goku achieve the Super Saiyan form early would fuel his jealousy and his desire to become stronger. He might even try to find new ways to train or gain power to catch up with Goku.
Well, he could change a lot of things. Maybe he'd prevent some of the big battles or save some characters who died. For example, he might stop Frieza from destroying Planet Vegeta earlier. It would be a whole new timeline with different outcomes.