In the spirit of the OP, and finding an enduring solution... something like the deadmans switch should be implemented in a de facto utility like browser passwor

In the spirit of the OP, and finding an enduring solution... something like the deadmans switch should be implemented in a de facto utility like browser password recovery but extended with a weighted audience tied to the time elapsed. Why not have that same function that keeps up with your authentications notify X audience in Y time - 30 minutes even or 30 years with an emphasis on how perpetual. Reasonably I say we all got a good hundred years to plan for.