You make an excellent case but it would be a brave author who could do this to one of her three main characters. I'm not sure I'd be able to do it - and I'm not adverse to bumping off characters when the need arises.

I think there may have been some scope for a fake death and rescue. You could've had your sad moment and rescued Hermione in a bittersweet Persephone way. Perhaps Ron could've done that, he had a bit of the ginger Orpheus about him. I think Rowling could've had her cake and eaten it too on Hermione, but I think she likely became too attached to her leads to bump any of them off.

I bet Fred was supposed to be Ron and she bottled it at the last second. These are the perils of narrative when you start writing a quirky kids book and end up with magical Saving Private Ryan.