I have an "In the Event of My Death" icon on my computer desktop, for my wife and kids. In that folder I have family stuff, but also a contact list of who to notify should I die. There are a couple folks on this forum in that list - I have a few email addresses and phone numbers I have squirreled away over the years. And the forum itself (using my login/password) hopefully will be notified. Not that anybody may care of my status, but it's just a forum post I have requested, so not a big imposition. So someday you may see a post from me informing you that I am no longer among the living. That will be weird, but don't freak out. I'm not planning to rise from the dead to type in a post, it will be from a family member using my login credentials. I should amend that folder name to be "In the Event of My Significant Illness/Injury"
I agree with Weedy that a master spreadsheet of people's contact info is probably a no-go. The mods could probably look this up from our initial account creation if they had to. But I'm sure there are many here just like me - when you join a new forum and know nothing about it, you give the registration process the least amount of personal information you can get by with. Later, you may trust the forum with more info, but initially probably not. e.g., If I was forced to give a phone number when I registered (I don't remember), be prepared to end up talking to some bewildered shop owner in Nigeria if you dial it. And you will probably find in my profile details that I an a 127 year old transvestite from Finland as well.
People could implement an informal "forum buddy" system though. Pick a buddy or two to keep tabs on and share contact info with. As frequent posters drift away from the forum as they inevitably will (e.g., Sentry), inform your buddy of your changing status, or your buddy can contact you to check up on why you're AWOL. Interests and situations do change, so there is no such thing as a lifetime forum member. We gotta expect that. Even the best of forums can eventually turn. I think many of us here originally came from a forum that we were long time members of, but that forum went downhill. Despite those forums having gone bad, there are probably still decent members there - not involved in the forum shenanigans - who are wondering where we went. I know that I left my old forum like that. I do a drive-by posting every six months or so to let them know I'm still alive - but nobody seems to care though, many of the other good folks I knew there left as well.