There are many ways to handle this in fanfiction. Some might write that a powerful artifact is found. This artifact has the power to restore life. The Straw Hats or other relevant characters then go on a quest to find this artifact and use it to bring back Ace or Sabo. It could also be that there's a prophecy in the fanfiction world which foretells the return of the fallen, and the characters work towards fulfilling the conditions of that prophecy.
Chapter 423, "A Scumbag!", is the clearest early answer because Hua Chinese Medicine gets a payoff that changes the stakes. The setup is Are you hurt?" Yu Li asked, panting., but the pressure keeps building through After receiving Jiang Li's message, he and Guan Xiong rushed back,....
Chapter 562, "So You Are Not First, But Last?!", is the clearest early answer because it turns Ai Xiaochun's situation into a concrete plot event. A useful checkpoint is the way the scene starts with After they finished preparing the fish, Guo Xing and Luo Xuan got...
Chapter 889, "Nice to meet you for the first time, please take care of me!", is the clearest early answer because it turns Ji Yanbai's situation into a concrete plot event. It opens with She said why do other prisoners get a chance to go outside, while she...
Chapter 515, "You actually kidnapped a man?!", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from After Miss Su Yinwan left in a huff, Shang Shuyue's mood greatly...
Chapter 910, "This place isn’t fun, I want to go home!", is the clearest early answer because it turns Dean Wan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Bufan was not very shy.
Chapter 389, "Slaughter Pig Platter", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 783, "I'll Fight it Out with You Rich People!", is the clearest early answer because the buildup finally cashes out in a real clash.
Chapter 599, "The Weather has Cooled Down, the Merchant Should Go Bankrupt", is the clearest early answer because it turns Shang Zhenhe's situation into a concrete plot event.
Chapter 754, "Evil Can Never Defeat Justice", is the clearest early answer because it turns Officer Xing's situation into a concrete plot event.
Chapter 522, "The First Test for the Scion of the Wealthy Family Has Arrived", is the clearest early answer because it turns Hua Country's situation into a concrete plot event. The setup is The assistant director's execution was swift;