Well, if Sally dies in a fanfic, it would be a huge turning point for Percy. Maybe he blames the gods more than ever. He could go on a quest not just for the usual reasons but to get some sort of revenge or justice. His relationships with other characters like Annabeth would also be strained as he's dealing with this massive grief. It would change the whole dynamic of the story.
In some fanfictions where Sally dies, it could lead to Percy being filled with a new kind of rage and determination. He might become more withdrawn at first, shutting out his friends as he grapples with the loss. But eventually, it could fuel his growth as a hero, making him more fearless in the face of danger because he has already lost the most important person to him.
One possible scenario in a fanfic where Sally dies is that Percy loses his connection to his 'normal' life. Sally was always his anchor to the mortal world. Without her, he might feel adrift. He could start to question his own identity more. Is he just a demigod or was Sally a big part of what made him who he is? This could lead to some interesting character development, like him trying to find a new purpose outside of just being a son of Poseidon and a hero.
Chapter 250, "Rescue, Intimidation, and Surprise (Part 2)", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. Early on, Those people in light gold armor have been using solidified fire oil.... By the end, That thing can actually eliminate dew, it's amazing!" Among the three....
Chapter 241, "Message, Rebellion, and the Strange Wu Xiong (Part 2)", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. A useful checkpoint is the way the scene starts with A crack opened at the base of the giant stone, revealing a pair of... and follows through with Once they reach the Beehive, they will then proceed south in batches....
Chapter 271, "Eliminated, Breakthrough Wave, Green Lotus Grass", is the clearest early answer because Xiang Ping finally turns buildup into a real advancement. The chapter gives readers a real answer by opening on Arena number three, tenth match for Meng Ning, starting now!" "Arena... and ending on Xiang Ping, fifth match, lost, eliminated!" "Zhou Yingkai, seventh....
Chapter 255, "Frenzied Fortune-Making, Dangerous Thoughts, Perfect Timing (Part 2)", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The setup is Hearing Xia Hong's words, Xia Chuan immediately nodded., but the pressure keeps building through He certainly wouldn't be so naive as to believe the two of them....
Chapter 181, "What Does Great Xia Want, Liu Dahu's Ambition", is the clearest early answer because it turns Liu Dahu's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The exchange meeting was still proceeding as normal, but unlike... and follows through with Five Ape Mountain!" Xia Chuan's demeanor was domineering, having been....
Chapter 298, "Hou Jing Surrenders, White Abyss Falls, Zhaoyang Changes Its Flag", is the clearest early answer because it turns Zhao Long's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Hou Kong is twenty-six this year, has a Superior Battle Body, and his... and follows through with Although called hostage, he was actually the disciple of Li Tianhua..
Chapter 232, "Saving Lives, Putting on an Act, Xia City in Uproar [8,000-Word Chapter, More to Come]", is the clearest early answer because the rescue effort creates visible on-page results. The chapter turns that into something concrete by moving from Peng Bo, a Superior Battle Body with the strength of Eight-maned, was... to Clang...… The staff came down for another fierce strike; though Peng....
Chapter 208, "Great Xia Sacred Pattern, Building Upgrades", is the clearest early answer because Xia Chuan finally turns buildup into a real advancement. The chapter turns that into something concrete by moving from Xia Hong first set his gaze upon the Fiery Sun Tripod in the center... to From the accounts of Great Xia's older residents, they've heard....
Chapter 254, "Alchemy, Special Envoy, Longyou", is the clearest early answer because it turns Solidified Fire Oil's situation into a concrete plot event. The chapter turns that into something concrete by moving from Solidified Fire Oil, truly a miraculous substance! to This is personally ordained by our leader, and we ask Xia Hong to....
Chapter 199, "Good News Keeps Coming for the Hong Gang Family (Part 2)", is the clearest early answer because it turns Hunting Department's situation into a concrete plot event. The chapter turns that into something concrete by moving from Husband Hong Gang is the captain of the Green Wolf Team of the... to Middle-aged women like her were nonexistent..