Gilligan interview pre-season 5. Revisiting the backstory has been discussed.
Q.
Given that Walt and Jesse know even less about Gus, and don’t know why he was so important that the cartel could not kill him, could their assassination of him come back to haunt them?
A.
That’s a good question. We will be getting into that when the writers’ room reopens in November. But I can think of one gentleman who may have a problem with it, who’s a bit closer to home, who is Mike, played by Jonathan Banks. [laughs heartily] Mike may have a problem with what transpired, and I wouldn’t want Mike mad at me, I can tell you that.
Giancarlo Stanton (pre season 5):
http://seriable.com/breaking-bad-gia...come-to-light/
Both Vince and Giancarlo have admitted that revisiting is a possibility. With Walt's family in likely danger and with Gilligan's promise for no loose ends...we will see.