I suppose it's inevitable at a certain point is life to look back and wonder what-if. I have a few. I choose to have children when I was in my early 20's. I had plans for my life, and set them aside with the reasoning that my youngest child would be grown when I was in my early 40's. Plenty of time to realize my dreams.
Then when the time came, what I realized was, I didn't want to do those things any more. What-if.
The second thing I didn't plan on was once my kids were grown and gone, I'd just have myself to take care of. I sort of forgot about my parents. It's different, but in many ways the same. I'm now starting to take care of them more and more. It's not really a what-if, I realize, but I didn't plan for it just the same.