Mr. Schuester would be in shock. He saw Rachel as one of his star pupils and a driving force in the Glee club. He would struggle with the guilt of not being able to protect her. He would try to keep the club going as a way to honor her memory, but it would be very difficult for him. He might also start a scholarship fund in Rachel's name for future Glee club members.
The characters would be devastated. Kurt, being one of her closest friends, would probably be in shock at first. He might go through a period of denial, thinking it's all a cruel joke. Then he would break down and cry, remembering all the times they shared together, from their fashion debates to their duets. He would likely be the one to organize a proper memorial for her, making sure it was as grand as Rachel would have wanted.
This type of fanfiction is quite heavy. It could depict Rachel's downward spiral leading to her suicide, perhaps due to the overwhelming grief of Finn's death. The writers of such fanfictions might focus on how the other members of the Glee club try to hold on to their own sanity while also dealing with the loss of two important people. It can be a very emotional read, full of heartbreak and a sense of hopelessness at times.
One possible plotline could be that Rachel succumbs to an illness. Maybe she has been struggling with a long - term health issue that finally takes its toll. Her friends in the Glee club are devastated and they come together to remember her through song, just like they always did when she was alive. They might perform a special memorial concert in her honor.
She could die in a car accident. Maybe she was driving to a big performance and got distracted by thinking about her career and future, and crashed. Another possibility is that she might have some sort of health issue that was never revealed in the show, like a heart condition that suddenly gets worse.
Mr. Schuester could be disappointed. He always saw Finn and Rachel as a power couple in the Glee club, their relationship inspiring others. He might try to mediate between them at first, but if that fails, he would hope they could both still contribute positively to the club despite the break - up.
Well, it would likely become more serious. They'd have to depend on each other more. Puck might become more protective of Rachel.
Rachel would likely start off as a bit of an outsider. She'd be nervous and eager to prove herself. As she gets more involved in the Glee club, she'd gain confidence. Maybe she'd start taking more risks with her performances and her relationships with the other club members.
Sometimes, Rachel could react by using her talent as a weapon against the bullies. She might sing a song that expresses her feelings of being bullied, hoping to make the bullies realize their actions are cruel. She could also turn to her friends in the glee club for support. If Finn or Kurt or Mercedes are around, she would likely confide in them and ask for their help in dealing with the bullies.
One common theme is grief. The characters in the fanfiction are likely to be overwhelmed with sorrow. They may also experience guilt, like thinking they could have prevented these tragedies. Another theme could be the shattering of dreams. Finn had his own dreams, and Rachel was so ambitious, and their deaths would mean the end of those dreams for them and also a huge blow to the dreams of the Glee club as a whole.
I'm not sure of specific popular fanfictions about Rachel Berry's death. Fanfiction can vary greatly in quality and content. Some might explore her death as a way to show the impact on the other Glee characters, like how Finn might react if Rachel were to die suddenly. It could also be a very dark take on the generally upbeat Glee universe.