Not to start the blog post off on a low note or anything...
Facebook wouldn't know that he died right away, though. My family isn't particularly tech-savvy, so it's possible that his Facebook page would persist in its current form for a while. Around the same time next year, Facebook might tell me that my cousin, though possibly passed on, is celebrating his 51st birthday.
My cousin's situation is not the first of its kind. There is a diverse range of traditions around the world for dealing with mortality, and the Internet has begun developing traditions of its own. With so many of our life experiences cataloged online in various ways, it seems almost expected that these windows to our lives would also provide constructs for our deaths.