If Vegito never unfused, it might mean that the enemies he faced were simply not strong enough to force the separation. This could imply that the story's difficulty level was lower than originally thought. Or, it could be that some external factor prevented the unfusing, creating a whole new set of plot twists and complications.
Goku being born with SSJ4 in fanfic would likely make him a force to be reckoned with from infancy. This could result in quicker power-ups, different battles, and maybe even a shift in the balance of power among the characters.
Some dedicated Dragon Ball fan communities on social media platforms might also be a good source. For example, certain groups on Facebook or Reddit where fans discuss and share their fanfiction works. However, the availability of exactly this pairing might vary. You may need to do some searching within those communities.
They often interact as powerful allies. They respect each other's strength since they are both the result of fusing two extremely strong Saiyans. For example, they might exchange fighting techniques or strategies.
It gives a chance for creativity in exploring gender - swapped or alternate versions of the characters. Fanfiction writers can play with the personalities and backstories of these characters in ways that the original series might not have explored. For example, they can write about how the female Vegito might approach a relationship with Gogeta differently than a male Vegito would, adding new layers to the story.
One scenario could be that Goku surprises Beerus with his speed and initial attacks as SSJ4. But then Beerus counters with his hakai and forces Goku to dodge constantly. Another could be that Beerus underestimates Goku at first and Goku manages to land some powerful blows.
Well, in many fanfictions, SSJ4 Goku is often depicted as having a chance against Beerus. SSJ4 Goku has shown incredible strength and combat skills. But Beerus has the power of a God of Destruction. His hakai ability could potentially wipe Goku out. Still, if the fanfiction is written in a way that gives Goku some new power - up or a special advantage, he could win. It really depends on the creative direction of the fanfic writer.
In some fanfictions, Gogeta and Vegito might find themselves in a different dimension where the rules of power and combat are different. They would need to adapt quickly. For example, they may lose their ability to fuse at will and have to rely on their individual skills more. This would lead to a great character - development arc for both of them as they learn to fight in new ways.
If Vegito stayed fused, it's likely that he could have overpowered the villains with his combined strength and skills. There might have been fewer challenges and a quicker resolution to the conflict.