Print, on good quality paper, can have a very long lifetime.
Since we are discussing digital files, why not print them out as, say, a linear series of periods and spaces ("." = "1"; " " = 0). I don't know how to do this, and I don't know how much surface on a piece of paper would be required, but it seems to me that this could produce a "permanent" (even if not fireproof) record.
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sj