If Naruto gives up on Sasuke in fanfiction, the storyline could take a very different turn. For one, the whole dynamic of their relationship, which has been a central part of the original Naruto story, would be completely disrupted. Naruto has always been determined to bring Sasuke back to the village. Without that drive from Naruto, Sasuke might become even more isolated and perhaps fall deeper into the darkness. This could also lead to different power alignments in the ninja world. Allies of Naruto might question his change of heart, and enemies could take advantage of the rift between the two former friends.
Maybe Naruto gets tired of always chasing after Sasuke. He has his own life and dreams too. He might think that he has sacrificed enough of his time and energy on Sasuke, and it's time to focus on himself and the village. He could start to believe that Sasuke has made his own choices and he can't keep forcing Sasuke to come back.
The story would take a very different turn. The dynamic between Naruto and the rest of the characters would change. For example, Naruto might become more focused on protecting the village without the distraction of Sasuke. His relationships with other friends like Sakura might also be affected. Sakura might be disappointed in Naruto at first for giving up, but then they could bond over the loss of Sasuke in a different way.
The dynamic between Naruto and Sasuke would be completely different. Instead of the usual pursuit, there would be a sense of finality. Naruto might start to avoid Sasuke, which would change the way Sasuke views Naruto too.
If Naruto gives up his dream, Sasuke might view him as a weakling. Sasuke has always been competitive with Naruto, and Naruto's giving up could make Sasuke lose respect for him. Their relationship could become strained as Sasuke may distance himself from Naruto, thinking he is no longer the worthy rival he once was.
One possible storyline could be that Sakura realizes Sasuke is too consumed by his revenge and she decides to focus on herself. She might start training harder to become a better ninja in her own right, perhaps specializing in medical ninjutsu even more. This could lead to her making new friends and allies within the village, and she could end up being a key figure in Konoha's development, without Sasuke in the picture.
One possible reason could be that Sakura realizes Sasuke is too consumed by his revenge and she can't keep waiting for him to change. She might see that he is constantly putting her in a secondary position and she decides she deserves better. For example, Sasuke has left the village multiple times, leaving Sakura heartbroken each time.
It could also be that he is tired of the false expectations created by fanfiction. In fanfiction, his character might be portrayed in ways that don't match who he really is. He wants to be true to himself and his ninja way, so he gives up fanfiction.
On a larger scale, it might change the way the story views the concept of unrequited love. Instead of the typical 'waiting for the loved one' trope, it shows that characters can move on. This can be an important message for readers, especially those who can relate to being in a one - sided love situation. It also might shift the focus of the story more towards Sakura's personal growth and her new goals, rather than the Sasuke - centered plot that it might have been before.
One possible reason could be that Naruto realizes Sasuke is too far gone in his quest for revenge. Naruto might see that no matter how much he tries, Sasuke won't change his ways, so he gives up. For example, if Sasuke keeps attacking innocent people in his pursuit of power to defeat Itachi's enemies, Naruto might finally lose hope.