I've not seen my dad for 24 years, parents split as soon as I left home, dad was always having affairs. He did send guilt money at Christmas, but I would send it back, I did write him a letter 5 years on asking if we could be friends, never heard a word. My eldest got in touch with him when she was 16, he got his other daughter to write back. But he has never tried to make contact with me. His loss, we have 5 grown up kids and grandchild number 5 on the way, I'm not sure what I would do if he got back in touch, but to be honest a letter explaining would be nice.
I would write a letter and see what happens, least then you have tried, as we get older we see life in a different light.