There are as many interesting stories about what happened to the cacti that have died or disappeared as there are about those that live on:
The Mother Cactus: If you've read the History section on this site, then you'll know that I bought this, original cactus, at a school fete in 1976. Over the course of the next few decades it flowered some 25 times and produced 70 something offspring. I thought it would last forever but I didn't consider that Roger, or rather "Wodger" as he pronounces his name, would remover the roof from the greenhouse I rented in 2008. Being temporarily housed in a dark shed didn't do wonders for the cactus family and many died without good light, warmth and fresh air. The Mother Cactus shrivelled up and couldn't be rescued. People often ask me if I was sad and I say "no", because it's all part of the tapestry of Day Of The Cacti. It's the same reason why I don't get upset if people tell me they've lost the cactus I gave them in a house move, or it "just died" or even that they "don't know what happened to it". It's all part of the story.
Referencing some of the years of neglect above, I found this beautifully constructed, empty bird's nest on top of several cacti in 2014.