What if I can't decide for myself, and I've written nothing down?

You have not written anything down. If the day comes when you cannot speak for yourself, someone else must guess. They will guess in fear, in a hallway, arguing with people who loved you differently than they did. This is not really about death. It is about a blank space where your voice should be. An uncarved block has no name, no shape, no use — until someone carves it. You can carve it now, calmly, or let panic carve it later, badly. Do this with your people, not alone in a drawer. A will, a directive, a note — these help only if someone else knows they exist. For the legal parts, see a lawyer or counselor; that is their craft, not water's. Your part is simpler: decide, write it down, tell your circle where it lives.