Gold will exist in 20 years, BTC not sure
But what will the value of gold be in 20 years?
The immutable value of shiny gold in 20 years will be the same as 1000 or 2000 years ago.
It will get you food, clothing, shelter, and intimate companionship.
Gold is proof of work, being born in a quasar or other extreme cosmic event.
SHA256 and ECC will be broken and forgotten long before we can duplicate the power of a supernova.
If you really think SHA256 will be broken, then you should be buying lead (bullets) and not gold. The entire financial network of the world is built on that encryption, ATMs, SWIFT, ACH, everything. If SHA256 gets hacked, it's the Mad max scenario and we will all have much bigger problems than bitcoin. Besides, we can migrate the blockchain over to SHA512 with a hard fork a heluva lot easier that the bank's 40 YO computer networks can upgrade. Perhaps you remember what a clusterfuck it was to fix the Y2K bug in 1999.