For Harry, it would be devastating. Hermione has been his rock, his intellectual equal. Without her, he would feel lost and incomplete. He might become more reckless in his fight against evil, as he no longer has her to rein him in.
One way this could develop is that Hermione's sacrifice could be a turning point in Draco's character. He might have been on a dark path before, but her selfless act makes him question his beliefs and actions. He could then start to work towards redemption, perhaps trying to fight against the dark forces in honor of Hermione.
Yang would be completely heartbroken. She'd likely go through a period of intense grief and anger, possibly even blaming herself for not being able to protect Ruby. Weiss would be deeply affected too. She might become more reserved and solemn, vowing to use her skills to uphold Ruby's ideals. Blake would be inspired by Ruby's sacrifice to be more active in fighting against the darkness. She might see it as a call to arms to make Ruby's sacrifice not be in vain.
In some fanfictions, a heartbreaking scene could be when Hermione says her final goodbyes to Harry and Ron. She might give them her most precious possessions, like her beaded bag filled with all their survival essentials, with a sad smile on her face as she tells them how much they mean to her.
One interpretation could be that it shows Hermione's selfless nature. She might sacrifice herself to protect Ginny from a great evil, like a powerful dark wizard. This act could also symbolize the deep bond of friendship between them, going beyond normal loyalty.
It can make other characters view their relationship as very exclusive. For example, Ron might feel left out sometimes if Harry is constantly overprotective of Hermione. This can create some tension between Ron and Harry in the fanfiction.
For Harry, it could be a huge blow. Hermione has always been his closest friend and advisor. Without her in the Order, Harry might feel lost and less confident in his decisions. He may start to question his own actions more, as Hermione was often the one to provide rational thinking.
Well, for Hermione, it would be a huge emotional blow. She might become more withdrawn at first, focusing on her studies even more to cope. Draco, on the other hand, might see this as an opportunity. Since it's a Dramione fanfic, he could start to approach Hermione more gently, trying to offer her support and gradually winning her over.
Their bond might make Ron jealous, which could strain Hermione's friendship with him. Since Ron has had feelings for Hermione, seeing her have this special bond with Viktor would be difficult for him. Other characters from Hogwarts might view Hermione differently too. Some might be curious and want to befriend her more because of her unique bond, while others might be a bit suspicious or jealous.
His friends like Ron would be extremely shocked and confused. Ron, who has always been by Harry's side, would find it hard to accept this new Harry. He might initially try to fight Harry, thinking he has been corrupted. Other characters in Hogwarts, such as the teachers, would be divided. Some might see it as a way for Harry to protect Hermione and understand his motives, while others would be strictly against his new path. The Order of the Phoenix members would also be split, as they have put so much faith in Harry as the 'Chosen One' to fight against dark forces, not become one.
For Draco, the emotional impact would be huge. He'd likely be filled with guilt, as Hermione sacrificed her life for him. He might also feel a sense of unworthiness, wondering why she would do such a thing for him. There would be a great deal of confusion as well, since they were not exactly on the same side before.