Thing is, if the pair had been hung they'd never have found Pauline Reade.

When Hindley was first arrested she was reported to have said to another prisoner "They'll never find them, they're up on the moors."

That may well be true regarding Keith Bennett because the moorland landscape changes and not only that, a pipeline has been laid there and if the actual pipeline didn't disturb his grave, the machines on the job could well have done and to cap that, if that didn't happen, the laying of the pipeline will have changed the look of the area so much that even if Brady had been told "If you show us where Keith is buried, we'll let you go" he couldn't do it because he couldn't pinpoint where it was.