There is no guarantee of any value. Not for gold, not for fiat currency, and certainly not for crypto. Up until Roosevelt there was a connected path between silver/gold the dollar and by extension to most of the rest of the worlds paper. Progressive dreams of empire broke constitutional money and created the third US central bank. US nationalized the banking system and shifted banking risk from bank shareholders to taxpayers. Bretton Woods nationalized gold holdings. Which Nixon defaulted on. Since then, the US dollar has been roughly speaking a petrodollar, backed by the empires constraint that all OPEC energy trading to take place in USD. Low cost oil and gas via fracking broke that market, in combination with China refusing to use dollars to buy US government debt. Which has spread planet-wide now, since no one has bought a Tbill since 2014 other than the Fed.
The fundamental problem is Triffin's dilemma. It impoverishes the working class while rewarding the political class, undermining all empires from the bottom. Because the world is using our money. Worth reading about.
A separation of currency and state (a return to constitutional money) would reverse Triffins Dilemma (combined with liberal trade laws, low tariffs) allow ordinary folks to return to wealth building activity that can't be co-opted by DC.
Ironically, crypto is good for the common man, and undermines the centralized command/control of the DC war machine. All empires have gone down the currency destruction path. Crypto might provide a more graceful, less fatal, glide path for this empire. Might. We shall see.