The sudden cessation of posting activity has happen on several occasions that I can recall.
We have (had?) one member, Marco Granati, who was a regular poster, especially on 65C816 stuff. He suddenly stopped visiting early in 2021. He and I had regularly communicated about the 816 and after not seeing any activity on his part or hearing anything at all from him for a while, I did a little digging to see what I could find out. I discovered a website he had for his projects had not been updated since early 2021 as well.
Marco lives in Italy, which as you may recall, seemed to be especially hard-hit by COVID, with a higher-than-average mortality rate. I sent him a PM to find out his status, which PM sat in my outbox for over three years...I finally deleted it. To date, I have no idea what has become of Marco.
Lee Davison, who was a member for many years and was the author of EhBasic, passed away in September 2013 at the age of 49. It wasn’t until July 2014 that anyone here knew about it—we learned about his passing by accident, although after some members’ efforts to contact him had failed, it was suspected.
Perhaps something should added to each member’s user profile that allows him/her to post some contact information...just in case. That info would be visible only to the forum administrators, who, at their discretion, could then attempt to make contact should that member suddenly go “radio silent.” I’m not familiar with the workings of the PHP software that runs 6502.org, so I don’t know how difficult it would be to add such a feature.