it depends on what the deal is with fiat, if there is a duel system, then fiat will always be in decline relative to btc, in which case, btc is still the ideal way to preserve wealth and use as savings.

if it's a btc standard in a world of no fiat, which i find hard to believe, then btc would be like gold back in the day, you have it, can save it, can spend it and retain purchasing power over the decades