In the long run, they might realize that they need to change their behavior. They could start thinking about how to make it up to Chichi. Maybe they'll go and do some nice things for her, like getting her some flowers or cleaning the house really well without being asked. This would show that they've learned their lesson and are trying to be better sons.
He might be surprised at first. After all, having his tail back is a big change. He could start to explore the new sensations and abilities that come with it, like better balance perhaps.
He might be a bit flustered at first. Gohan is not the most confident when it comes to romance. He could stutter a bit and then take a moment to compose himself before responding positively. He might say something like 'I've always hoped for this, but I'm just so surprised right now' and then go on to express his love for her.
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.
Gohan's power of transformation could be affected. Instead of turning Super Saiyan in the normal way, it could be related to the haki system in One Piece. Maybe his Super Saiyan form gives him a special type of haki that is unique and extremely powerful.
Gohan may become more confident in relationships. In a harem situation, he has to deal with multiple people interested in him, which could boost his self - assurance.
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.
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.