Yes, Michael could definately rejected the life, and he did while his father was still healthy and in charge. While it is true that no one has to take command as a successor, Michael, the son who was the most like Vito, realized himself that he had to step into the business in order to save the family, while it was his own choice, he basically saw within himself that he really did not have a choice at that point. He knew that he was the one who could save the family. We also see that Michael took the attempt on his father's life personally, took McClusky's assault that left him disfigured personally, and the coldness that was deep within him rose to the top and he now desired to cold bloodedly murder Sollozo and McClusky to: A) save Vito's life, and: B) get even with McClusky at the same time. There is no doubt in my mind that if Vito had not been shot and remained healthy, that Micahel would have taken the legitimate road in life. But then again if that happened we would not have the story!

Don Cardi