There will always be usage for the dollar in the world which cannot be changed overnight since because of war. But during this kind of situation, the safer asset will always be Gold for the general public who doesn't believe in crypto. But people who believe in crypto will either have all into BTC or split across BTC and gold. The US Fed will not allow the dollar to drop a lot in that situation they use their reserve of other currency to buy dollar which will curb the dollar selling pressure.