This sort of situation makes me very glad that I have some very close friends IRL from the boards. My parents would know to contact them if anything happened to me, and I expect that they would let everyone else know.
I think a memorial sticky would be a lovely way to remember people who are no longer with us.
I read somewhere that in your will or other important documents, it's advisable that you leave any log in details, forums, anything important online so they can be updated/informed when you pass and they can possibly shut things down or delete stuff for you. Or you can have an information sheet for online stuff that only a good and trusted friend will know where so they can handle it when the time comes. Sad but a good idea.