"Ernst Blofeld was never killed by James Bond. In For your eyes only James is visiting the grave of Tracy, while he is called by M. M sends him an helicopter and a new training for Bond begins. On the roof of a building is a dummy in a wheelchair. It must appear it is Ernst Stavro Blofeld. Bond never got over the dead of Tracy, so M16 designed a project to simulate the death of Blofeld.
So that in FYEO was a training.....
Years later we see in Casino Royale the sinistre Mr. WHITE. he has a special organisation with "people everywhere". Also he comes back in Quantum... and dissapears without getting killed. So that is why everything is open to let Blofeld alias willard white to comeback......."