This is more of a trust issue. Americans were trusted previously because they upheld free market, justice, fairness, human rights etc... From the confiscation of private Russian assets in America and around the world, it showed free market, justice and fairness can be trampled under their feet so long as it fits Americans narrative...without any regard to law. Have to say, the Americans did themselves in. Then the collapse of credit swiss and the American banks... The Swiss government failed again to respect free market proceeding where bond holders precede shareholders in credit. Again, who dares to put money in Swiss banks any more? Nevermind there weren't much left to go around for the shareholders. American decoupled USD from gold years ago, now, they just need to print more USD to save their banks and all the USD holders around the world have to pay the price(devaluation of USD) for the willful and irresponsible actions of the Fed!!! All these are lost of credibility of the Western economies headed by America.
Yes, USD is hard to be replace without any credible contenders. However this decline in USD as global reserve will continue simply because people and the world found they cannot trust and be held hostage by Americans any longer.