I saw my ex for the first time in 20 years one evening last summer..I was driving home from work and he was walking the opposite direction. I'm owed a zillion explanations on behalf of my daughter who he abandoned in favour of someone other woman's kids, and also my daughter became a super successful in her both her private and business life as well as being a lovely human being and I wanted to tell him how he'd missed all of that, I'd thought about it many times over the years.....I briefly braked , he looked around at my car and I could see there was no recognition in his eyes, and then in seconds I changed my mind and drove on the 500 hundred or so yards to my house . I had no idea that he was in this area, the last I knew he was living 2 towns away...came to discover later that he's been living literally 1/4 of a mile away for the last few years with yet another wife..
I felt guilty immediately that I hadn't taken my chance and stopped and demanded answers for my daughter, so as soon as I got indoors I called her and explained, and said I was sorry that I'd had the chance to speak to him and didn't take it, and did she wish I had...she was appalled, and told me that as far as she was concerned he was dead to her, we owed him nothing, ...that I'd raised her single handedly with no emotional support or financial help from him from our divorce when she was just 8 , we'd always lived in the same house he knew where we were yet he chose not to contact her..so she doesn't ever want him to be any part of her life.
the irony of it all is that he turned his back on his first born, and all the children (3) that he had and raised with other women have turned out to be no good wasters
Sad, but I totally understand her..so in answer to the OPs question if I were to pass him in the street, I would have to ignore him because I couldn't possibly speak to him without raising the subject of our daughter and I have to abide by her wishes.