Perhaps Harry discovers a new magical ability within himself just as he's about to be overcome by the dementors. This could be some form of advanced Patronus charm that he didn't know he was capable of, which he then uses to fend them off. In this fanfiction, it might also lead to him having a deeper understanding of his own magical heritage and the power he holds.
One possible plot development could be that a powerful magical creature or a hidden ally steps in at the last moment to save Harry. For example, a phoenix might appear and drive the dementors away with its purifying fire.
In some fanfictions, the situation could lead to a change in the relationship between Harry and other characters. For instance, if Hermione was nearby when Harry almost died to the dementors, she might become more protective of him in future situations. This could also cause her to research more about dementors and find new ways to combat them, which could be a major part of the ongoing story.
One possible plot development could be that Voldemort fully regains his power without Harry as an obstacle. The wizarding world would be plunged into complete darkness. His friends, like Hermione and Ron, might go into a deep state of despair and then form a resistance group. They would try to find other ways to defeat Voldemort, perhaps by seeking out more powerful magical artifacts or uniting with some previously neutral magical creatures.
One possible plot development could be how the wizarding world reacts to the loss of the so - called 'Chosen One' even as a baby. There might be widespread grief and fear among those who opposed Voldemort, as they had placed so many hopes on Harry. Another aspect could be how Voldemort's reign of terror continues without the threat of Harry Potter. He might become even more powerful and tyrannical, with no one to oppose him in the way Harry was prophesied to.
Maybe Dumbledore. He is extremely powerful and has a great deal of knowledge about dementors. He could arrive just in time, using some mysterious and powerful magic that we haven't seen before to rescue Harry. His presence would also add an element of mentorship and guidance as the story progresses.
One possible plot development could be that Sakura's tears somehow give her a newfound strength or resolve. Maybe she decides to train harder to protect Naruto in the future. For example, she could seek out a powerful teacher or a hidden jutsu to become stronger.
One possible plot development could be that with Harry's death, Voldemort fully takes over the wizarding world. His reign of terror becomes absolute, and the remaining characters have to go into hiding or form a secret resistance. For example, Hermione might lead the resistance, using her intelligence to try and find a way to defeat Voldemort without Harry. Another aspect could be the emotional turmoil among the characters. Ron would be devastated, and his character could either sink into depression or be driven by a thirst for revenge. Ginny, too, would have to deal with the loss of her love and might become a more hardened and fierce fighter against the Dark forces.
One possible plot development could be that his friends are left to pick up the pieces. They might struggle with grief and guilt, thinking they could have saved him. Another could be that Voldemort finally takes over completely without Harry to oppose him, leading to a dark reign over the wizarding world.
One possible plot development could be that Hermione is left with a deep sense of guilt and responsibility. She might then take on Harry's mission or cause in his memory. For example, if they were fighting against a new dark wizard, Hermione could become even more determined to defeat the enemy.
One possible plot development could be that his death shatters the Straw Hat crew. They might disband in grief, each going their own way. Zoro could become consumed with revenge, vowing to take on the Marines who were responsible.
One possible plot development could be that when Percy dies, his friends are devastated. They might embark on a quest to find a way to bring him back. In the process, they discover some long - hidden secrets about the gods. Another development could be that Percy's rebirth gives him new powers, which he then uses to fight a greater threat that was emerging even before his death.
One possible plot development could be that the Hidden Villages struggle to maintain peace without Naruto's influence. His death might lead to power vacuums and political unrest. For example, some villages may try to take advantage of Konoha's weakened state. Another aspect could be how his friends and family cope. His wife, Hinata, might have to raise their children alone, and his friends like Sasuke would feel a great sense of loss and perhaps guilt for not being able to protect him. The ninja world as a whole could also lose its hope symbol, and new, darker forces might emerge, thinking that without Naruto, they can carry out their evil plans more easily.