Elaine H from December 05 and Laura from July 2010 sadly aren't with us anymore. Elaine passed away in 2007 (Andy K posted on here to announce the news) and Laura was in her early 30s and fighting cancer at the time, but sadly passed away 2 years later in October 2012
The most well-known example of this was Frank who did 4 shows in March 2010 and almost instantly became a big character. Then on his 5th show, Frank was absent due to illness, and at the end of the show, Noel announced that after Frank left because of his health, he sadly passed away not long after.
I remember a few months later, there was an old man on the wings named Mike who disappeared halfway through his first show due to poor health and never returned - i sometimes wonder if something awful happened to people like him as well (along with Audrey and Clive from the early days of the show, who disappeared after a handful of shows on the wings and were nowhere to be seen after that, and also Mandy who did a handful of shows in 2015 before leaving and not returning)