It sounds like your dad was one of those people who did it right, with pretty much everything in his life.
I wasn't able to be there with my Dad when he passed- he just went to bed two days before Christmas 2018, and never got up the next morning. I was so happy that he was able to be in the home that he loved, until his very last day.
I get it, completely, as to what dementia can do. Mom passed in 2012, and she really had a bad time from dementia. It got to be, to where she just didn't remember or recognize anyone, at the end. And I think it frightened her, to no end, to sense that she should be able to remember the people around her- but she just couldn't. I almost feel like it was more merciful that she passed away, rather than being in that state anymore.
I sense that you are a bit like me- in that you are choosing to primarily remember the great things that your Dad did, just like I choose to remember what Mom did, rather than the state she was in at the end of her life. Like my Mom, your Dad sounds like someone you can be really proud of...
Regards,
Gordon.