Better Call Saul executive producer Peter Gould has discussed how the prequel will jump back and forth through time, enabling the writers to bring back characters that were killed in Breaking Bad, possibly including Walter White himself.
Here's what Gould told the New York Daily News: "One of the great things about having a time line which is flexible is that perhaps some of it takes place before Breaking Bad, during Breaking Bad, and after Breaking Bad. That gives us the ability to bring back characters that were killed on Breaking Bad."
Of course, this doesn't necessarily mean it will be Walt who is resurrected in the spin-off (Breaking Bad's list of dead is pretty long after all), though it would make sense given what a profound impact he goes on to have in Saul's life.
The story of how the lawyer came to be in business with Gustavo Fring might be more easily worked in though, while Breaking Bad survivor Jesse Pinkman we know also knew Saul during his earlier years given it was he who introduced Walt to him.
Aaron Paul previously said he hadn't been offered a role on the show (though was very keen for one), while Bryan Cranston teased "Never say never" as to a return to Walter White.