Anyone have a recommendation for a good killswitch, notify my next of kin, delete my browser history sort of service? There's lots of things I want to make sure I say to the people I care about if I disappear but I have no idea how to ensure that happens.

Your trusted notary, usually.

You mean I have to rely on a human?!

Yes, because they are also able to fix any problems in the plan you came up with, in faith of your wishes.