In some fanfictions, Rey might die due to a tragic misunderstanding. For example, the Resistance could misinterpret her actions as being in league with the enemy. As a result, they attack her, and she is mortally wounded before she can prove her innocence. This would be a very dark and angsty take on her character's end.
Another idea is that Rey succumbs to an ancient Jedi curse. There could be a hidden curse within the Jedi lore that gets triggered when she delves too deep into an old and forbidden Jedi power. This curse slowly drains her life force as she tries to fight against it, but in the end, she is unable to overcome it and dies, leaving the galaxy in shock.
One possible storyline could be that Rey sacrifices herself to defeat a new and powerful dark side threat. Maybe a Sith Lord emerges who is far stronger than any before, and Rey realizes the only way to stop him is by using a dangerous and self - destructive Jedi technique that ends up costing her life.