I guess estrangement happens for many different reasons, but until you thrash out the whys and wherefores with the person concerned I would think you never get real closure.
My father estranged himself from my mother soon after they married and while she was carrying me. I went through life in the 60s and 70s not seeing him, although I had to perversely write him monthly letters about my life. His slippers and coat were left lying around in pretence when visitors came to the house. Luckily he lived abroad in Hong Kong which was so alien to me he could have lived on the moon, or dare I say it, have been dead. All very strange. He resurfaced for my wedding, I was polite and accepted his presence. He then reappeared when my mother died, a month before my first child was born. I resented him holding the baby, it should have been my mum, but once again I was courteous and dutiful. I did worry he was trying to make some form of amends and would work his way back into my life, but he left for Australia to live there. I think he was riddled with guilt and regret after 25 years of estrangement. He sadly drowned himself off the beach in Perth. How did I feel? Of course upset, but more because I was left with neither parents nor siblings at a youngish age. It was the bigger picture that saddened me. So once again I picked up the pieces, but the final straw was when he left his money, (a very wealthy man), to his sister, again not caring about my existence nor my baby. History had repeated itself, I could do nothing. I moved on and have had the happiest marriage and the loveliest children I could have asked for.
Thank you for listening. 35 years later it still helps to off load the story.