Well, it's a really interesting question, and one that I guess could be solved with a smart contract. I'm not quite sure how it would work, maybe there could be some kind of dead-mans trigger, which requires certain inputs to occur. I wonder if there is a business opportunity for someone to create an semi-automated system which does actually have human interaction for being able to do a manual check? I guess if public records were on the blockchain it may make it easier (until some hacker decided to mark you as dead, then marry your sister or something...?). It's a really interesting concept, and one which I look forward to seeing solved.