I haven't come across a particular 'naruto dies saving sasuke fanfic' myself. However, you might want to check Naruto - centered forums where fans discuss and share such stories. Maybe by asking around in those communities, you'll find what you're looking for.
In many Naruto fanfictions, Naruto saving Sasuke from darkness is a popular theme. One aspect could be that Naruto uses his unwavering friendship. He constantly reminds Sasuke of their bond, like the times they trained together as kids. Naruto's positive attitude towards life and his dreams of becoming Hokage also inspire Sasuke. For example, Naruto might show Sasuke that there is more to life than revenge, and that by working towards a positive goal, he can find true happiness and purpose.
In this fanfic, Sasuke could sense Naruto was in a dangerous situation with Sakura. Maybe Sakura, under some dark magic influence, was about to harm Naruto unconsciously. Sasuke, with his quick reflexes and strong power, rushed in between them. He used his Sharingan to break the magic's hold on Sakura and saved Naruto. Then Naruto and Sasuke had a moment of understanding, looking at each other with a new level of respect and friendship.
One possible plot development could be that Sasuke is in a life - threatening situation, perhaps against an extremely powerful enemy. Naruto sacrifices himself to give Sasuke a chance to escape or defeat the foe. This would likely lead to Sasuke being filled with guilt and regret, and might change his whole outlook on life.
One possible plotline could be that Naruto has to go through a series of dangerous trials in the enemy's territory to reach Sasuke. He might face powerful foes and have to use new jutsu he's developed. Another plotline could be that Sasuke is in a coma, and Naruto uses his chakra to somehow enter Sasuke's mind and fight off the inner demons that are keeping Sasuke trapped. Maybe Naruto also has to convince Sasuke's friends from his time away to help him in this rescue mission.
One interesting fanfic could be 'Sasuke's Redemption in Saving Fem Naruto'. In this fanfic, Sasuke discovers that Naruto, who is female in this version, is in a dangerous situation. He uses his newfound powers and his sense of loyalty to rescue her. It shows a different side of their relationship, with Sasuke being more protective.
One consequence could be a change in the relationship between Naruto and Sasuke. Sasuke might become more enraged or, on the other hand, he could start to question his actions. As for Naruto and Ami, their bond might grow stronger. Ami would likely be very grateful to Naruto, and this could lead to a closer friendship or even something more in the future of the fanfiction.
A possible plot is that Sasuke is in a different dimension and Naruto has to figure out a way to travel there to save him. He might have to gather some special items or learn new jutsus to make it possible. Or perhaps Sasuke has lost his memories and Naruto has to help him regain them while protecting him from those who want to use his amnesia for their own gain. In some fanfics, Sasuke could be in a coma and Naruto uses his own chakra to try and wake him up, which could lead to some really emotional and intense scenes.
One emotional moment could be when Naruto makes the final decision to sacrifice himself for Sasuke. His friends are left in shock and disbelief. The moment of his death is often filled with his thoughts of all the good times and his unwavering belief in Sasuke's redemption.
The ninja world is often left in a state of shock. Naruto was seen as a symbol of hope, so his death could lead to a sense of despair among the younger generation. Villages might start to question their alliances and the future of peace that Naruto was striving for.