I will give my own personal prediction on how I think Jimmy McGill will transform into Saul Goodman;
At the end of Season 2, Chuck secretly recorded Jimmy's confession and has it on tape. At some point in Season 3, Chuck will bring the tape to Jimmy's attention in an attempt to blackmail him; either change your name and never do law again, or the tape goes public and he will go to jail. Jimmy will ultimately choose changing his name. James McGill Esquire is no longer doing law and is now Saul Goodman. Knowing that he cannot do law anymore, Saul gets in contact with Mike and asks him if there are any jobs available for him, as he is no longer a lawyer. I'm sure we will see Saul and Mike do jobs together for Gus Fring. However, I do not believe Saul will actually meet Gus himself, as he said he did not on Breaking Bad. Gus is very careful with whom he does business with and is hard to get in contact with. As Saul does jobs with Mike under Gus' employment, Kim will eventually become fed up with Jimmy's change and cut ties with him. This causes Saul to become depressed, as he lost the love of his life and blames Chuck for it all. He will then try and sabotage Chuck once again to get revenge and will cost Chuck his law career. Then at some point, Chuck will die. Possibly from a heart attack or maybe suicide. This will cause Saul to feel a tremendous amount of guilt for his brother's death, feeling he was somewhat responsible for it. Saul and Kim have one last conversation before the two ultimately part ways. Saul decides to continue law, but will be a crooked lawyer as we see in Breaking Bad.
I could be wrong, but I think in the end, Saul Goodman's birth will be as a result of Chuck. What are your guys' thoughts?