He might meet the future versions of Naruto and Sakura. Their relationship with him could be very different in the future, perhaps they are now leaders of the village and Sasuke has to adjust to their new status.
One common theme is Sasuke's struggle to admit his feelings. When he's jealous, it shows that he actually cares more about Sakura than he lets on. Another theme could be misunderstandings. He might misinterpret Sakura's interactions with others as something more than friendship.
His understanding of relationships might grow. Through his interactions with Sakura, Sasuke could learn about compromise, forgiveness, and unconditional love. For example, he might learn to forgive himself for his past mistakes and understand that Sakura loves him despite all that.
In these fanfictions, Sasuke often becomes more responsible. He was once a brooding and solitary ninja, but as a baby daddy, he has to think about someone other than himself. For example, he might start to plan for the baby's future, which is a big change from his usually self - centered ways.
Sasuke's character often develops in terms of his loyalty. By saving Naruto, he shows that his loyalty to their friendship is growing stronger. He may start to question his previous lone - wolf attitude.
Their relationship could start off very tentatively. Sasuke, being so used to solitude, might be a bit standoffish. But Hinata's gentle nature could gradually break down his walls. They might start with simple exchanges, like Sasuke noticing Hinata's Byakugan abilities during a battle or training session. This could lead to a mutual respect, and as time goes on, they could become friends and perhaps more depending on how the story progresses.
In some fanfictions, there are scenes where Sakura is in danger and Sasuke realizes just how much she means to him. For example, if Sakura is injured while protecting Sasuke, Sasuke's reaction of guilt and his newfound determination to always be by her side can be an extremely emotional part of the story.
One possible reason could be that he overestimated his abilities during a battle in the Wave arc. Maybe he took on an enemy that was much stronger than he thought and got fatally injured. Another reason could be that he sacrificed himself to save Naruto or someone else. It's also possible that there was some sort of betrayal within the group they were with, and Sasuke was caught off - guard and killed.