Taking it all is one thing. Being able to hold it is something altogether different. In a war of attrition, The U.S. and it's allies would be able to beat China. They just simply don't have the techinology, the training, or the deep pockets to win a protracted military conflict against the West. If we had to, we could get by without income from the Chinese markets. Wouldn't be fun, but we could do it. China would go broke fast if funds from Western trade went to zero.
We need to assume that in a worst case scenario, it's not China alone, but an Axis with the SCO at its core. Also assume overland moves in Europe concurrent with ones in Asia. In other words, assume, worst case, most of both Asia and Europe are taken early on by the Axis and we have to fight WW2 but worse. Assume also, that very early on, something happens simulataneosly to the Straits of Hormuz and Malacca. And being the dark scenario guy that I am, I also personally assume that nuclear weapons ranging from tactical to strategic, are used to eliminate military targets, including Diego Garcia, early on and that the nukes are from the combined SCO arsenal.