Yes. The conflicts between Sanji and Luffy in the manga often stem from complex circumstances and character developments that drive the narrative forward.
One great fanfiction could be about their adventures on a new island not shown in the original story. Maybe they encounter a powerful and strange new enemy. Luffy's determination, Zoro's strength, and Sanji's culinary skills all come into play in this new situation.
Another theme is rivalry. Zoro and Sanji have a friendly rivalry which can be elaborated on in fanfictions. For instance, they might compete in a friendly tournament on the ship to see who is stronger or more useful in a certain situation.
As of now, Sanji is very much alive in the One Piece manga. The story keeps unfolding with him as a vital part of the plot. The author hasn't written his death yet.
One Piece was a very large comic and animation work, which described Luffy's family story in a very wide range of plots. Luffy's father was Admiral Zoro, his mother was the pirate Nami, and he had two older brothers, Choba and Franky, as well as an older sister, Nicole Robin. In One Piece's storyline, Luffy and his family experienced many adventures and challenges in pursuit of the dream of becoming One Piece.