Yes, he had choices at every point and made the wrong choice. I don't know if Puzo and FFC deliberately framed it that way but it certainly appeared to be the case. It reminds me of a similar theme in Tolkien's work-that evil blinds those seduced by it.

Michael makes the wrong choice from the beginning and then sees other choices become worse and worse although he's making "rational" decisions all along.

I don't know if the other Families would have easily let him get out of the life once he murdered Sollozzo and McCluskey. Certainly the attempt on his life in Sicily showed that Barzini was keeping an eye on him. Once the ceasefire was attained, Michael could certainly have declined to become boss in waiting. It would have upset his father but that wouldn't have been the first time.

However it would have been accomplished an army of hoodlums, police and private detectives at the hospital protecting Vito until he was well enough to be moved home COULD have worked without Michael having to murder.