I see no downfall or hubris in their decision. I do, however, see extreme arrogance in your comment. You've decided that just because you don't consider senil

I see no downfall or hubris in their decision. I do, however, see extreme arrogance in your comment. You've decided that just because you don't consider senility or incompetence to be horrible that nobody else should either. Those two people made a reasoned decision about what they wanted their lives to be like and what they wanted to happen when they could no longer live the way they wanted to. Thankfully their children, who obviously didn't want to lose their parents, understood that being forced to continue living with declining mental and physical capabilities was a fate worse than death to their parents, and did not interfere.