It could lead to them becoming an almost invincible force, easily defeating most enemies.
If they stayed fused, their combined powers and skills would likely create all-new challenges and adventures. They might face even more powerful villains or explore uncharted universes.
In fanfiction, if Goku Black fused with Goku, it could potentially create an extremely powerful being. This new entity might have a mix of Goku's pure heart and Goku Black's more sinister motives, which could lead to a complex internal struggle. Their combined power could be off the charts, perhaps strong enough to defeat any foe in the Dragon Ball universe. However, it could also cause chaos as their different personalities clash within the fused form.
Well, it could be really cool. Naruto's ninja skills combined with Vegeta's Saiyan power would make for an extremely powerful being. Maybe they'd have Naruto's ability to create multiple clones and Vegeta's energy blasts at the same time. They could also inherit Naruto's determination and Vegeta's pride, which would make for a very interesting personality mix.
It could lead to some major power-ups for Goku. Maybe he'd learn new fighting techniques and strategies from Vegeta's unique style.
In fanfiction, if Goku and Vegeta go back in time, they might change the course of history. For example, they could prevent some of the villains from ever becoming powerful. They may also meet their past selves, which could lead to some really interesting battles or training sessions. And they could introduce new techniques to their past counterparts, making the Saiyans even stronger earlier in the timeline.
Well, they could change the entire timeline. Maybe they'd go back and team up with their younger selves to take on foes that were previously too powerful. They might also influence the relationships between characters. For instance, Vegeta could potentially have a different attitude towards the Z - fighters earlier, which would change the dynamics of their group. It could lead to a whole new set of adventures and battles that we haven't seen in the original story.
They might change the course of history and prevent some major disasters.
Their fused form might have Goku's spiky hair, but with some of Goku Black's purple - tinted highlights. The body would be muscular like Goku's, but with a more menacing stance similar to Goku Black. The clothing could be a combination of Goku's orange gi and Goku Black's black under - shirt, maybe with some red accents added in for an extra pop of color.
Perhaps Vegeta kidnaps Goku to get some secret training method from him. Vegeta is always eager to become stronger, and he might think Goku has some hidden knowledge that could help him surpass his limits. So he takes Goku to a secluded place to force the information out of him.
Well, if they were brothers in a fanfic, it could change how they interact with the other characters. Maybe they'd have a deeper understanding and fewer power struggles between them. Also, their family background and upbringing could be explored in new and interesting ways.
It could lead to all sorts of interesting storylines. Maybe they'd have powerful kids or face new challenges together as a couple.