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.
Sasuke is very likely to be involved. He has a close relationship with Naruto and is also an important figure in Boruto's life. His skills and knowledge could be crucial in any adventure or situation that Naruto and Boruto find themselves in. Another character could be Hinata. As Naruto's wife, she would surely be concerned about any strange events involving Naruto. And for Boruto, she is his mother, so she would play a role in any family - related or village - threatening situations.
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.
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.
The most popular characters in 'Boruto meets Naruto fanfiction' are Naruto and Boruto, as they are the main focus of the concept. However, characters like Jiraiya can also be very popular. His connection to Naruto and his own legendary status add depth to the fanfiction. Shikamaru is another character that fans like to see in these stories. His intelligence and laid - back attitude can create some interesting interactions with the main characters.
One possible interesting plot could be Naruto and Boruto getting transported to a parallel dimension where their roles are reversed. Boruto has to deal with the challenges Naruto faced in the past, like fighting powerful villains without the advanced technology he's used to. Meanwhile, Naruto gets to experience the modern ninja world from Boruto's perspective, including the new ninja tools and different social dynamics in the Hidden Leaf Village.