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.
In a 'Gohan kidnapped by Raditz' fanfiction, the plot could involve Raditz trying to turn Gohan against his family. He could expose Gohan to the cruel ways of the Saiyan race that Goku has somewhat distanced himself from. Raditz might show Gohan visions of the Saiyan's former glory and try to convince him that his human family is holding him back from achieving true power.
One plot idea could be that Gohan's friends, like Krillin and Bulma, team up to rescue him. They might use some of Bulma's inventions to track Raditz. Another idea is that Gohan manages to outwit Raditz during the kidnapping. Maybe he uses his hidden power to escape Raditz's clutches briefly and leaves a trail for his father Goku to follow.
Goku would be a mix of angry and worried. His Saiyan blood would make him want to rush into battle with Raditz right away. But he also knows how dangerous Raditz is, so he might first try to gather some allies, like Piccolo. He'd be constantly thinking about Gohan and how to rescue him as quickly as possible.
If Raditz survived in fanfiction, he would likely have a complex relationship with Goku. He might start to see the value in Goku's way of life. Goku could try to reform him, and Raditz could slowly become a more positive force in the Dragon Ball Z universe.
A good Raditz story should focus on his Saiyan heritage. For example, showing how his Saiyan instincts play out in different situations, like when he's facing a tough enemy or making a decision about whether to show mercy or not.
If Raditz turned good, it might have led to more complex character dynamics and interesting plot developments. He could have learned from his mistakes and become a valuable ally.
Raditz could be redeemed by sacrificing himself for the greater good. For example, if there was a powerful enemy threatening the Earth and he steps in to take a fatal blow meant for someone else, like Gohan or Goku.
Family ties are a key element. Since they are brothers, fanfictions often explore their complex relationship, like how they deal with their Saiyan nature versus the influence of Earth. For example, in some, Goku tries to make Raditz understand the importance of protecting the planet.