The ninja world as a whole could experience some changes in the field of jutsu research. Orochimaru was a master of many forbidden jutsu and his death might mean that some of his knowledge is lost forever. However, it could also open the door for new types of jutsu development as ninja try to fill the void left by Orochimaru's absence.
For Naruto personally, he might face some internal conflict. Even though Orochimaru was an enemy, killing someone is a big deal. Naruto might struggle with the morality of it all, especially if he had to use extreme measures. He could also face some external backlash from those who were secretly in league with Orochimaru or those who thought Naruto should have found a more peaceful solution.
One consequence could be a shift in the power balance among the ninja villages. Since Orochimaru was a powerful and feared figure, his death might cause some chaos as his former allies or subordinates try to either avenge him or claim his resources. For example, some of his secret labs and experiments might be up for grabs, leading to potential conflicts.
One consequence could be a shift in the power balance in the ninja world. With Orochimaru gone, his followers might scatter or try to seek revenge. This could lead to new conflicts.
Since Orochimaru had many experiments and secrets, his death at Naruto's hands in the Chunin Exams fanfiction could lead to a scramble for his research. Other villages or even some rogue ninjas might try to steal his notes and facilities. In Konoha, Naruto might be pressured to reveal what he knew about Orochimaru's plans and secrets. This could put him in a difficult position as he may not know everything. Also, Sasuke, who had a connection with Orochimaru, might have a complex reaction. He could be angry at Naruto for killing Orochimaru, or he could see it as a sign of Naruto's strength and be motivated to become stronger himself.
In some fanfics, Naruto might use his new and powerful jutsu that he has mastered over time. Maybe he combines his Sage Mode with the power of the Nine - Tails in a unique way that Orochimaru can't counter. For example, he could use the Nine - Tails' chakra to enhance the range and power of his Sage Mode attacks, and then catch Orochimaru off - guard.
If Mizuki kills Naruto in a fanfic, it would likely have a huge impact on the Hidden Leaf Village. Naruto was seen as a symbol of hope, so his death could lead to widespread despair. His friends like Sasuke and Sakura would be deeply affected, perhaps Sasuke would be even more consumed by revenge. Also, the Nine - Tailed Fox inside Naruto would be a major factor. It might go on a rampage or be captured by the wrong people.
One possible consequence could be chaos. Naruto was often seen as a symbol of hope and peace. His death at the hands of Madara would likely shatter the dreams of many characters. The villages might descend into fear and distrust again, and there could be a power vacuum that leads to wars between the different ninja villages.
The immediate consequence would be the destruction of Konoha, which is a major power in the Naruto world. This would create a power vacuum that other villages might try to fill, leading to possible wars and political unrest.
He could be feared by the remaining ninja. Since he has killed all his enemies, others might see him as a ruthless killer rather than a hero. This could lead to isolation as people would be scared to approach him.
One possible motive could be power. In some fanfics, Sasuke might be driven by an insatiable thirst for power and see Naruto as an obstacle. Another could be revenge, perhaps believing Naruto has wronged him in some way in that alternate story. Or it could be a matter of being corrupted by dark forces, which make him turn against Naruto.
In a fanfic where Orochimaru kills Naruto, the plot would take a very different direction. Naruto was the Jinchuriki of the Nine - Tails, and his death would mean the Nine - Tails' power is lost. Orochimaru might try to take over Konoha or use Naruto's death to gain some other advantage. The other ninja villages might see Konoha as weak and attack. His friends would have to deal with the grief and might turn to different paths, some perhaps darker in their search for meaning after such a loss.
Well, in some versions, Naruto might use his new and improved Rasengan techniques. He could have combined it with his Sage Mode powers to overpower Orochimaru. Maybe he also uses his quick thinking and the element of surprise, since Orochimaru is always so full of his own schemes.