As of now, Naruto and Sasuke haven't died in the Boruto manga. Their characters continue to play significant roles and contribute to the story's development.
In a lot of fanfics, Naruto is stronger than Sasuke. Naruto has always had an incredible willpower and in fanfics, this can be translated into him achieving greater power levels. His ability to make friends and allies can also lead to him getting more support and resources in the story. For example, he might get some special training from an ancient sage that Sasuke doesn't have access to. Also, his positive attitude can attract more powerful beings to help him out, which gives him an edge over Sasuke in terms of strength.
Boruto's character development could be a complex journey. At first, he may feel overshadowed by his parents' fame and power. This could lead to him acting out or trying to prove himself in the wrong ways. However, as he experiences more of the ninja world and faces challenges, he starts to understand the true meaning of his parents' actions. He might develop a more empathetic side, seeing things from the perspective of others, especially those affected by Naruto and Sasuke's past actions. He also grows in terms of his combat skills, learning from both his father's brute force and Sasuke's finesse. His character arc could be about finding his own identity within the context of his parents' great reputations.
Naruto is stronger in fanfiction because of his ability to connect with others. He has made friends all over the ninja world. This network of friends often provides him with support in battles, whether it's intel or actual combat help. Also, his training under Jiraiya was very comprehensive. Jiraiya taught him not only combat skills but also how to be a better person. This made Naruto grow both physically and mentally. And compared to Sasuke, Naruto seems to be more adaptable to different fighting styles in fanfiction, which gives him an edge in combat.
Sasuke often appears in different story arcs of the Boruto manga, depending on the current plot and mission. Sometimes he's on a solo mission, sometimes he's involved in events related to the village.