I've tried to mitigate this risk by keeping a so-called "death book": a hardcopy of all accounts, passwords, 2 factor auth instructions, router SSIDs, and so on, kept in the firesafe with all the other important stuff. But this Reddit post points out that this is not enough! Someone would also have to come in and take over the technical toil and maintenance that it takes to keep everything running. Not sure what the solution is. The rest of my family has no interest in learning this stuff. They can't even remember their own passwords without me, let alone ssh to our VPS and restart exim4.