It may not be a world without the Fidelius Charm; Lupin implies that the betrayal of a secret keeper was still what did them in. It may simply be that the charm may Never Be Mentioned Again, because if it’s allowed to function as more than a one-time plot device, it breaks the story, so we’re just going to have to shove it in the corner and pretend it’s not there anymore.
It may not be a world without the Fidelius Charm; Lupin implies that the betrayal of a secret keeper was still what did them in. It may simply be that the charm may Never Be Mentioned Again, because if it’s allowed to function as more than a one-time plot device, it breaks the story, so we’re just going to have to shove it in the corner and pretend it’s not there anymore.