I’m still a bit split on this. And whether the complexity and reliability is good enough for the use case… I mean if you don’t need N-out-of-M, but it’s just two people: cut a password or key in half. Same if it’s N-out-of-N people, you just need to make some puzzle pieces and hand them out, we don’t really need encryption and fancy maths for that. But I guess encrypting something would work, too. Just use a program or algorithm that’s likely still around when it’s going to be used. And you can always add a sheet of paper or PDF with instructions. Maybe save the executable file to to decrypt it somewhere if the solution requires software.
By the way, concerning the loose surge protector: Good thing you replaced that. If you see something like that, and it’s mains voltage, always replace it ASAP. Not because it doesn’t look nice or the RasPi gets unhooked… But because it’s a proper fire hazard. A whole house can burn down if you have a loose mains connection and that somehow leads to electrical sparks.