"...what to save, gold coins, heads of cattle, food in the cellar."

The more things change, the more they stay the same.

"...bitcoin will not be around for long. (we really need better terms for ages/cycles.) It will probably be less than 100 years..."

Within 5 years BTC will be slave coupons, only usable for what overlords allow. KYC and digital biometric ID are rolling out now with extraordinary rapidity, and these allow the physical network(s) our communications - including transactions - ride on to be granularly controlled by the owners of that infrastructure. What is the value of a BTC if you aren't allowed to buy anything except cat food, or high fructose corn syrup, or pay the rent on a bugpod in your 15 minute prison, with it? What use is the cryptographic security of XMR if you aren't allowed to xmit encrypted data, and so can't spend or buy any? Cryptocurrency is CBDC, just without the CB's and straight banksters instead.

"...something of financial worth."

Financial worth won't exist for we plebs. UBI and social credit will replace it for 15 minute prison inmates, and the rest of us will care about real wealth, actual goods and services that create the blessings of civilization, and the social communities that make them valuable.

Thanks!