If Izuku stops holding back in fanfiction, he might achieve his goals much more quickly. He could show his true power and skills without restraint. For example, in battle scenarios, he could defeat his opponents with ease and surprise everyone around him.
Perhaps the writer of the fanfiction is trying to create a different character arc for Harry. Maybe he has faced so many hardships that he becomes disillusioned. For example, if he has lost too many loved ones and feels that his efforts are in vain, he might stop trying. It's a way to add a new layer of depth to his character.
Perhaps when Natsu stops holding back, it would also have an impact on his relationships. He might be more assertive with his friends or show a different side of his personality. In the fanfiction, this could create some interesting character development and new storylines. For example, his more forward attitude could lead to some misunderstandings at first but then deeper bonds in the long run.
The plot would likely become more action - packed. With Natsu not holding back, there would be more intense battles and challenges. Enemies that were once difficult to defeat might be easily overcome, which would then lead to new and more powerful adversaries emerging.
The bullies might face some form of punishment from the Hogwarts faculty. Since Harry is well - respected, his report of the bullying would likely be taken seriously. They could get detention, lose house points, or even be suspended. Also, they may face social isolation as the other students might look down on them for their mean behavior.
One possible reason could be that the author wants to create a sense of mystery. By making Harry Potter stop talking, it makes the readers wonder what he is thinking or feeling, and adds an air of enigma to his character. Maybe he has witnessed something so shocking that he is rendered speechless for a while.
Perhaps Harry teams up with some of his friends from Hogwarts. Ron could use his strategic thinking, and Hermione her vast knowledge of magic. Together, they create a magical trap for Ebony Maw. Harry, being the main hero, would be the one to lure Ebony Maw into the trap and then use a powerful combination of spells to stop him.
The plot takes a darker turn. Without Harry's determination, the fight against evil might seem almost lost. His friends would have to scramble to fill the void he leaves. For example, Hermione might become the main driving force, but she would face many challenges without Harry's leadership.