Charlie has certainly come full circle on the island and in his life. The redemption theme is definitely showing itself to be prominent with him. I have had mixed feelings about him in times past, however he has turned out to be one of the least selfish characters. He made his peace with Sun, he has put Claire and Aaron ahead of himself. Maybe Desmond kept saving Charlie's physical life until he could make things right in his life, which in the end is what really saves a person.