Why does it need to be scanned years later? I suppose if you are mitigating the risk of going to prison or something like that, then it might make sense.

But either way, you can print to paper and store it in a fireproof safe (or probably better still -- a safety deposit box). There are lots of methods for ensuring printed paper survives for a long time -- if you google it, I'm sure you'll find more than you want to know.

My personal method is storing passphrase encrypted on multiple USB drives (they're cheap) and replacing them every year or so (they're cheap).

I think a more interesting question is: how do I provide access to my non-technical wife in case I am incapacitated or dead? Especially, how do I convince her not to put the passphrase on a sticky note on the fridge?