My mother was adopted by her maternal grandparents, after the TPR of both bio parents resulting from abuse and neglect. Since the illness and death of both of my grandparents, we have been in more consistent contact with my aunt (the bio mom). She has finally straigthened her life out: no drugs, her current husband is not abusive like the previous ones

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This progress with her has made me consider contacting D (the bio dad). He was the abuser in the situation and, at the last contact, had not changed. He was an opportunistic manipulator. The last time we saw him was over 20 years ago. When he couldn't get anything from my parents, he disappeared. After a few years, he began to send birthday cards to us. He often wrote letters and made promises that were never kept--you know the drill, I'm sure everyone has heard this type of thing. In any event, he insisted that I call him grandpa--that was the last straw. I was 8 years old the last time he wrote me a letter telling me to call him this. Without my parents knowledge, I wrote him a letter telling him that I would like to know him because of our genetic connection but I already had grandparents. I wanted a realtionship with him as a person, but I didn't need him in that capacity.
In any event, my mother doesn't seem interested in finding D but says she doesn't mind if I do. Because my aunt has changed her life, I often wonder if he has. If he is interested in a relationship, between two adults (not as grandparent/grandchild), I think that I would like to meet him again. However, I am concerned about what could happen if he has NOT changed. I have two little boys to protect. Is the risk worth the chance of making a connection with him?
Any help will be appreciated.