That's part of what makes the hospital scene at Vito's bedside so poignant. Is Vito's tear when Michael tells him "I'm with you now" one of happiness or sadness? I think some of both.
W, I interpreted that scene as Michael's telling Vito that I am a son who has not always acted like a son. I have refused to follow your direction; I've gone my own way. I still intend to go my own way, but the estrangement is gone. Dad, you need me now as a father may need a son and I am here for you.
In other words, as some have opined otherwise, I need not interpret Michael's words as Michael's commitment to the Corleone criminal life.
