The death of a loved one can be difficult, especially when their online life continues to exist. A British funeral service called R Hyde Chambers has created an infographic to help the bereaved know what's what on social media sites if you're trying to wrap things up for someone or if you're planning for yourself. More on the infographic can be found here.
Also, apparently services in some countries offer more for those who wish to close out their online lives. Japan's Yahoo! is now offering Yahoo Ending. Once the search engine receives an official notice of death for a user, it will delete all his or her Yahoo Japan data, cancel any charges to Yahoo’s digital wallet, expunge files from Yahoo Box online storage and send farewell messages to loved ones."
The search terms "estate planning" and "social media" used together don't bring up much in the library catalog---consider whether this is because no book exists on the subject or no law exists on the subject. But that doesn't mean there isn't information out there. In fact, this area is so new, you might consider writing a law review note on it. If you do, feel free to stop by the law library reference desk for tips and suggestions on gathering your sources.