Frankly, all of those people should just go die because the world would be a MUCH BETTER PLACE without people like them. Even the MC who became nice in the end AND tried to own up to his wrongs at the time doesn't deserve forgiveness since he was the worst while she was still protecting his feelings. In fact, the deaf girl deserves acceptance into sainthood for all they did while the rest of her classmates simply deserved a very early death!
If someone has legitimately realized they've made a mistake and want to make up for it there is no reason to not allow them a chance other than to be petty.
I'm not too sure how to feel about the ending as I don't think the male MC learned anything from it and his explanation that everything happened because "You suffered because no one could hear your voice" and "All we did was hurt each other. We never used our voices." smacks of victim blaming as he turns her into the person who started it and from a victim to a culprit and himself into a victim of her actions. Especially the latter can only refer to her not picking up her soaked notebook, the abuse he suffered by the hands of his classmates and their fight in the hallway.
I really don't get how that's victim blaming at all. He's not saying she was at fault for it. He was saying that because she couldn't actually talk and because no one else was willing to use the notebook there was a huge lack of communication. It's clear he thinks that the classmates are the ones completely at fault for it. (And the teacher doesn't look to be remotely innocent either.)