Back to the original post, I think Michael died alone in Sicily because he either pushed everyone away from him, having learned his lesson, or everyone else pushed him away, having learned their lesson. Either way, Michael was alone in every meaning of the word.

Kay probably never recovered from Mary's death and never wanted to see Mike again. Connie probably saw what she was becoming and swore off the life and Vincent, too young and selfish to see what this life could do went back to NYC and was eventually killed when he got into the drug game.

But who knows. Maybe after Mary's death Vincent did what Turnbull is alluding to and got out of that life -- made the decision that Mike had several chances to make. But we'll probably never know.

What we do know is Mike was alone. After Mary's death he probably shut down completely. It looks like he even went blind.