Sounds similar to credit reporting services. You lose your wallet and call them, and they call everyone else.

It does sound like a very good idea, so I ran a search to see if anyone had done anything like it yet.

The general category seems to be "online death notification services."

Here's one called <a href="http://www.deathswitch.com/ rel="nofollow">"Deathswitch."

If you fail to enter a password at regular intervals, the system assumes you're dead or critically disabled and fires messages in all directions.

Useful for some circumstances, but I could see opportunites for unfortunate outcomes for absent-minded users who go on vacations...