well i think that's not possible but even if for some reasons we imagine something like that to happen then it would be just like a dictator holding all the fiat currency and not letting it circulate in the market and then obviously the money he's holding will have no value or will become just worthless so same thing should happen to the bitcoins too eventually they would also become worthless if there were left none of it with anyone of us but all of them were in just one person's possession, it would become worthless I guess and there are whales in bitcoin market who buy large amounts of coins but no whale is crazy enough to buy the entire supply as who will they sell it to later on as no one will be interested in bitcoin then