One possible scenario could be that Percy dies heroically in a battle against dark wizards. Maybe he sacrifices himself to save his family or a group of innocent people. Another could be that he succumbs to a mysterious and incurable magical illness that has been plaguing the wizarding world. He might have been researching a way to stop it but in the end, it gets the better of him.
Perhaps Percy dies in an accident at the Ministry of Magic. There could be some sort of dark magic experiment gone wrong or a terrorist attack by dark forces. He could be in the wrong place at the wrong time and lose his life while trying to protect his colleagues. In a more emotional scenario, Percy could die of a broken heart. After years of estrangement from his family and then finally reconciling, he might not be able to bear the thought of losing them again due to some new threat and uses all his magic to protect them, draining himself in the process.
Well, Percy might die in a magical accident. Maybe he's trying to harness some extremely powerful and unstable magic, and it backfires on him fatally. He could also be the victim of a curse. A powerful sorcerer or a vengeful god could place a curse on him that slowly kills him. And in some fanfictions, Percy could be killed by a group of enemies who gang up on him when he's in a weakened state, like after a previous battle or when he's separated from his friends and allies.
One reason could be to add more conflict within the Weasley family. Percy was already somewhat of an outcast in the family due to his loyalty to the Ministry. Turning him into a Death Eater would intensify that divide.
In some fanfictions, Percy Weasley may be depicted as a Death Eater, but this is a departure from the original canon. Fanfiction allows for creative reinterpretations, and some authors might explore this dark turn for his character to add drama and new plotlines.
One possible scenario could be that Percy has faced so many traumas and losses in his battles against the monsters and gods' schemes that he simply feels exhausted and wants an end. For example, if he loses his close friends like Annabeth in a particularly brutal way, it might push him to the edge.
Maybe there's a powerful, ancient monster that Percy battles single - handedly to keep Artemis safe. The monster could be something like a Titan that has been awakened and is far too strong for Percy to defeat alone.
It would be a huge blow to the Weasley family. They would be filled with grief and guilt, especially if they had any unresolved issues with Percy before his death. For example, if they had been on bad terms due to Percy's past actions at the Ministry. His death might make them more determined to fight against the dark forces, seeing it as a way to avenge Percy.
One common scenario is that Percy spies on the Death Eaters or other dark wizards for the Ministry. His knowledge of wizarding laws and regulations could give him an edge in infiltrating their ranks or gathering information about their activities.
In some scenarios, they might die heroically in a big battle against dark forces. For example, while protecting Hogwarts, they could be outnumbered by powerful dark wizards.
One reason could be his regret over his past actions. For example, when he distanced himself from his family to pursue his career at the Ministry. He might realize later how wrong he was and cry out of remorse.
Perhaps it's a symbol of his new - found independence. After leaving his family and then potentially coming back, he might be exploring new things. Smoking could be part of that exploration, something that he wouldn't have considered before. Also, it could be used to add an air of mystery or edginess to his character. Fanfiction writers often use such elements to make a familiar character seem more complex and interesting.