I'm only on the 4th book of Harry Potter but my friend is just a spoiler and told me that Fred will die. I personally think that the story'd end better if Fred is alive, well, the twins are my fave characters. But I think it will make the story more realistic, well more realistic in the fiction world (what? XD), I hope you understand what I'm trying to point out. A story must have its ups and downs, and, unfortunately, one of the downs is Fred being killed.
I'm not trying to make a fight, in case that's how you'll interpret my commenting on your comment. I'm just trying to put Rowling's point-of-view on why she had to do it... hopefully (((: