Bella might go into a deep depression. She was so in love with Edward, and his death could shatter her world. She could become withdrawn and isolate herself from her friends and family.
Edward would likely be in a state of panic. He loves Bella deeply, so he'd probably do everything in his power to save her. He might search for a cure or a way to reverse whatever is causing her to die.
Edward would be completely devastated. He would likely go into a blind rage and seek out whoever was responsible for Bella's death. His love for her was so intense that he would stop at nothing to avenge her.
There are other fans who are interested in exploring different storylines. They see it as a creative way to expand the Twilight universe. They might enjoy seeing how the characters would react in such a difficult situation, even if it's not in line with the original story.
She might be devastated. Bella was deeply in love with Edward, so his leaving would be a huge blow. She could cry for days and feel like her world has ended.
Edward might be extremely protective. He already has a strong urge to keep Bella safe, but with the added connection to the Joker, he'd be on high alert. He might be worried about the Joker's influence on Bella and try to keep her away from that part of her life.
Edward might be a bit disappointed as he values responsibility. But he would also offer to help immediately because he cares about Bella. He might say something like 'Let me take care of this, Bella. You don't need to worry.'
Well, in 'bella sees the future fanfiction', one aspect could be the impact on the plot. If Bella can see the future, it could completely disrupt the original storyline. Maybe she sees a future where a character she loves dies, and she goes on a mission to change that fate. This could lead to a lot of new adventures and challenges that weren't in the original story. Also, it could change how the other characters view her. They might see her as a prophet or be scared of her new - found ability.
He might be really surprised. Naruto is used to his own world and the fanfiction could show things he never imagined. For example, if the fanfiction has his kids achieving great things in new ways, he'd be proud yet a bit shocked at how creative fans can be.
He might be shocked at how the village has developed. In some fanfictions, the village could have advanced technology. Naruto, being from a more traditional ninja world, would likely be both amazed and a bit confused at first.