Yes, my state now is not a representative state of the one I was in a year ago before my health started failing. But I'm still the same person. I forgot that briefly after my terminal diagnosis, and starting doing things I thought were the right things (making sure things would be OK for my wife, tidying up a litany of messes that would be hard for her to deal with without just giving up and selling things for pennies or giving them away), but after a few weeks and speaking to the right people, I started living more normally again.
Yes, my priorities have changed massively - things that I thought were important 4 months ago are truly meaningless to me now - but many things that are important to me now were so before. And they will be until I cease to exist. I'm making the most of the time I have left because it's important that my experience at this point is as good as it can be, and because I want my wife to have good memories of our last months together.
I've never suffered from 'reason 2'. I've always felt I made the right decision at the time with the information I had and the person that I was at the time. So I don't have many regrets - none of significance to speak of, certainly. I know I am lucky in this respect.
Reason 3 is meaningless, IMO - both generally and certainly to me. I'm 53.
And I don't think many people really do think about this seriously until it's actually on the table for them. I certiainly know I didn't - even last year when I had an operation which hopefully would have removed the cancer and given me years of life, I hadn't really thought about the finality of death and what it means (or doesn't) to me. FTR I'm an Atheist, and I think that 2026 will have as much meaning/experience for me as 1969 (i.e. before I was born).