Fading is the right word. But at some point the competition for world dominance will cause instability that will break out in world war. Russia knows this and that's why it's using MacKinder's heartland theory to consolidate its power in their former border states. Look up MacKinder in Wikipedia. His theory states that the world consists of one big island (Eurasia-Africa) and whoever controls the world island is strategically situated to control the world.
Without the USA buying stuff from the Chinese sweatshops China will revert to its old methods of keeping people under control - pruning theirpopulation through starvation. They have no need for war. War gets you more people to control. China doesn't need more people. They need space and raw materials. Russia has what China needs but war with Russia would be suicide because Russia could quickly bring all of China's progress to a halt by using a few of its thousands of nucelar weapons. A world without a strong USA would be under Russia's nuclear blackmail.
This scenario could unfold quite rapidly in todays technology dependent world.