No one can predict the future, and this is sensationalism and speculation, not reasoned journalism. Let's talk about the "fall" of the UK. The British have universal healthcare and London is a leading global city. The biggest things that can be said for bad about the UK are (1) that London is extremely expensive, and (2) that the weather sucks. (1) is true but hardly seems to have anything to do with global decline;…
The question is: what happens when empires fall? And there is no answer to that without knowing that replaces them. The British lost prestige, and actual power, but gained a favoured seat at the new game's table. Presuming a world dominated by China, where does America fit in? I have no idea. I agree that its likely -not- going to be catastrophic, but there are just so many unknowns, and so much depends on exactly what kind landing there is.
And as inciting as the idea of the global elite who lord over us regardless of our nationality... I don't think the Chinese would appreciate a bunch of white guys "running" the show afterwards. Just as generations of Western Europeans and Americans where able to enter regions and dominate or co-opt the local elite through superior resources and means, the Chinese will do the same.