I'm afraid I don't have one of the "positive stories" you're looking for, but how it all turned out has certainly made me feel much better and able to move forward.
My biological father was married to my DM, but left for another woman when I was 2 and DSis was a new born - wiping out both DM's current and savings accounts and leaving us penniless. We saw him a few times a year until he remarried when I was about 5, then he vanished into the ether with his new wife and had 3 more children.
We next heard of him again through my DG (his DM), who told us he'd like to see us and for us to meet his other DC. He had just left his wife for another woman (are you sensing a theme...?) and seemed to suddenly remember he had two other children. DSis was not interested, but I was 16, and wanted to get to know him and my half siblings. The first few times we met, he made me feel like I was the most important person in the world, and I felt so special and like I really mattered to him. All that made it all the more painful when he dropped out of sight again after a few months. He'd pop up every few years and the same cycle of him being sorry for not being in touch, being over the top with attention and affection and then suddenly disappearing would continue.
When I was pregnant with my first child, he moved to a town 30 minutes away with wife number 3, and he appeared repentant for all his poor behaviour over the years and there were promises of being much better if I would allow him to get to know his grandchild. This time, we were in touch for around 3 years (mostly due to the efforts of his wife, who was lovely), but when he left her - I bet you can guess why - he fell off the map again. When the kids were primary age, he turned up on the doorstep one day, close to tears at the "shame" he felt for being "such a shitty father" and he begged me for the chance to make it up to me and my DC. He was wonderful, the all singing, all dancing father I'd always wanted! It lasted just shy of a year.
A couple of years later, he got in touch and asked to see me and the DC and I told him he would have to earn it. All I asked from him was a phone call every couple of months and to send a card for my 2 DCs on their birthdays and at Christmas. I made sure he knew when their birthdays were and that he had our address. Then I waited for his call. Guess what... No call, no cards, no anything.
7 years later, on Christmas Eve, I was out collecting one of my DC from a party and had a random mobile number come up on my phone. I answered it on handsfree and there was his voice, booming around my car "Olive? Olive, it's Dad!" I was so shocked - I hadn't heard from him in years and didn't honestly know if he was alive or dead! I told him I was in the middle of something, and would call him back.
I got home and started thinking about it. I didn't want to call him, I was fine without him and I knew he would only bring more upset in the long run, but then I felt guilty for not responding, how silly is that? After all the times he had let me down, here I was, allowing one phone call from him to take over my thoughts and start to ruin my Christmas. Then I got angry! I decided to write down every single memory of each time he has let me down, how abandoned I'd felt as a child, how poor we were when he left, stealing my DM's savings and refusing to pay a penny in maintenance. It was really cathartic just to get it all out. Then, I decided to just send it to him, and I did. I decided that if there was ever any chance of us having a relationship, then he needed to know how badly he had hurt me, he needed to accept and apologise for what he had done before there was every a chance for us to move forward and I knew if he couldn't do that, at least I'd feel better for getting it off my chest. True to form, his response was rubbish; "Sorry... goodbye.", but I think he got the message, and I feel SO much better!
So, not positive in the way you were hoping, but it certainly feels positive to me! Some people are just not worthy of being parents, and I'm sorry you've had to go through this too. Please try to remember that his inability to be a decent parent is not a reflection on you.