There's some fraction of people who would prefer to be kept alive as a brain in a jar, depending on the alternatives, but getting to that point is going to require a bunch of people to volunteer to undergo excruciating torture as we learn how to keep the brain alive, how to keep them comfortable, how to keep them conscious, sane and let them interact with the world.
I don't remember where specifically I learned this, but I was taught that tissue has to be alive to be useful, so they harvest it when you're almost-dead. Having my last moments be being literally dismembered is not something I wish for my future self.
I hope this is a comforting answer, I choose to be an organ donor because of these details.