Nutshell version:
Jimmy Johnson and Jerry Jones co-existed initially because both needed each other. Jerry needed a coach who could change the culture of Dallas; Jimmy needed an owner who would do anything to make Dallas a winner.
But as Dallas got successful, Jimmy resented Jerry meddling, and Jerry resented Jimmy trying to insinuate he knew nothing about football.
Jimmy Johnson wanted out of Dallas. He forced his way out by saying disparaging things about Jerry Jones, who took the bait and claimed, and I paraphrase, "Any 500 coaches could take Dallas to the Super Bowl."
Jimmy "faked" offense, and the two parted ways. Despite the view of other Cowboys fans who felt Jerry chased Jimmy away, I never faulted Jerry Jones. Jimmy was a shrewd coach, a manipulator, and that worked for him in establishing the Cowboys as a powerhouse, especially given their relative youth. But Jimmy orchestrated his exit from the Cowboys. He wanted to return to Florida. Initially, he wanted the Jacksonville position, but I don't think Jerry would let him go. But he really wanted the Miami position, and he wanted to exit Dallas to be in a position to get that job.
Jimmy Johnson will not come back for the very reason he's gone. Jimmy likes being considered a legend. He is a master manipulator. He wants to ALWAYS be considered as the coach who built the Cowboys dynasty and led them to back-to-back Super Bowls. If he comes back and doesn't achieve that, he sullies that image a bit.
I've always said, you leave on top and leave them wanting more. I thought Sugar Ray Leonard should have done this. He not only beat Thomas Hearns and Roberto Duran, but he got in their psyche so much that they wanted rematches with him to exorcise personal demons. Sugar Ray should have left them pining over the opportunity to fight him again. He didn't. He got greedy, and now those wins over Duran and Hearns, while classics, don't allow him to maintain the psychological mastery over his top two rivals.
Jimmy aint gonna do that. He wants fans to talk about him with reverence and associate him with the glory years. He loves nothing more than to hear fans say ... "Jimmy Johnson would get this team in shape. We haven't had a great coach since Jimmy Johnson."
Jimmy will never coach this team again. Book it.