That will only happen if the Russians decide to attack Ukraine. Which is highly likely. Now Ukraine has an extremely small army and they would not be able to defend for sure. It's important to actually sort these things out because at the end this could not just involve Russia and Ukraine but can also cause the start of a new world war. If this can be attained by doing things like sanctions and not deploying the troops and fighting on the border then I do think that's good. Their currency is falling and I do think that cryptos would be helpful for the people during this time.
I don't think if Russia occupies Ukraine then America or NATO will be fully involved in the war. They can co-operate with Ukraine with arms and money. Even when Russia occupied Crimea, we did not see any US or NATO direct involvement in the war. America knows very well that the situation is not the same as before. Even if the United States were ahead in terms of a single power, if Russia and China joined together, the United States could lose its leadership over the world. Inflation and corona attacks are also destroying the US economy. In such a scenario, America would never want to engage in a war where their interests are not directly harmed.
That will be a political decision that would cut their own face..as they say. The rest of the world accepted the US Dollar as a global reserve currency, so they would effectively harm those countries too. The other countries might be neutral and a decision like this will alienate them and they will also start with sanctions and/or trade restrictions against these countries.
It is not impossible to do this, but the ripple affect in the global economy will do them more harm than good in the end. China and Russia are dependent on a lot of resources from other countries too.
If they really take such a measure then they will surely build an infrastructure to replace US dollars supremacy. They just can not declare that they will accept the US dollar no more which will be politically inconvenient for them. But Russia already suffered due to US sanctions to them over the decade and still manage to survive that harsh conditions. So I will not be surprised if they really take such a measure with china and other Anti-USA countries.
China became the world's largest economy and the USA economy weakened due to history's worst inflation, Putin and Xi Jinping could see this as an opportunity to destroy USA dominance over the world.