You don't even need to trade oil, trading gulf country assets also works well. And rebuilding the gulf should be quite profitable if Iran blows it up and the assets will be available cheap.
Sure. If you go back 80 years and past several pointless wars you can find one example. Wherein the USA fought with a world wide coalition to defeat the Nazi's only after war had been declared by the Nazi's against the USA.
Actually, you can just look in Iraq, and CNOOC, PetroChina, and Zhongman. Companies will benefit, just not American ones.
And the US will clearly have failed to protect allies and project force in the Gulf. If the bulk of OPEC moves to a basket currency trade to ally more with PRC, India, and Russia that will be an astonishing failure.
I wouldn't have thought even Trump and this Republican administration was incompetent enough to break the petrodollar, but here we are, just one year in.
Also, don't look at fracking production curves. Bakken and Eagle Ford are foreshadowing the Permian.
I can see this war being mismanaged enough that gulf countries go to sell in yuans straight. After all, aligning with china will prevent further attacks from iran and almost all the stuff being made in the world already sells in yuans.