My thoughts: Governer obviously had eyes on the prison. He wants to kill Rick and the other leaders, but he wants Michone alive (no doubt to horribly torture). He would have known Michone wouldn't be with them, so it's not in his interest to kill Rick yet. After their sitdown, Gov realizes what buttons he can push to get both things he wants: Michone delivered and the heads of the snake cutoff. Diplomacy isn't always about peace, rather it can actually be a very effective tool of war. You lull the other side into a false sense of security, then BOOM, blitzkrieg.