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.
The first chapter of the Godlike Heroes List, Daji, did not specifically mention when she died, so the time of her death was not clearly stated in the novel. However, in the plot of the novel, Daji was used by the officials of the Shang Dynasty and eventually became a demon girl of the Shang Dynasty. She was destroyed by the army of the Zhou Dynasty.
From a scientific point of view, it was impossible for a person to see the Black and White Ghosts before they died. According to the authoritative medical journal Lancet, the visual and auditory perception at death was caused by brain disorder and did not really exist. Hallucinations or mental states before death may cause some people to see or hear strange scenes, including the black and white impermanence, but these scenes are just hallucinations or psychological reactions of the dying person, and there is no conclusive evidence. Therefore, from a scientific point of view, people would not see the Black and White Ghosts when they were about to die.
Sakura would be completely devastated. She's been in love with Sasuke for so long and has a deep bond with Naruto too. She might go into a deep depression and lose her will to be a ninja for a while.
The Naruto novels typically take place within the timeline of the Naruto universe, often filling in gaps or expanding on events that occurred during the main story.
The possibilities of where we go when we die in Soul Eater fanfic are endless. It could be a fantasy world, a place of judgment, or even a realm of rebirth, all crafted by the creativity of the authors.