The US isn't anything like traditional historical empires for one. It hasn't built its prosperity on invading other nations to annex them and plunder their national wealth, which is traditionally how empires temporarily sustain themselves. The US built its immense wealth today (just under half of all private wealth on earth is owned by Americans) overwhelmingly through invention, engineering, industry, trade, manufacturing, radical productivity gains spanning two centuries, and lots of immigration. Historical empires have always run out of lands to conquer and wealth to steal from other nations, and then they collapse as they fail to placate their own people or get defeated militarily by the lands they previously conquered.
The USD global reserve is a vulnerability? That's one potential issue. However, the US was the world's largest economy - by about 1890 - long before it had the global reserve currency. Japan has a disastrous situation on its hands economically, and a currency they're very aggressively abusing, and yet they're still the world's #3 economy with a substantial GDP per capita. The notion the US would just wilt without the global reserve currency, is absurd.
What lands has the US annexed that it's going to get pushed out of (and lose the plunder/tax from said nations)? What nation/s is the US stealing all of its prosperity from, such that that is going to end soon? Are we taking $5 trillion annually from Vietnam and Mexico (it's actually the other way around given the vast US trade deficit, we're sending hundreds of billions to the rest of the world)?
Further, the US was the first Capitalist nation. From day one it was heavily built on the principles of the free market and trade, not invasion and plunder. (and before anyone chimes in to loudly proclaim that the US has never been a perfect Capitalist nation: no kidding, such wasn't implied) Otherwise there would be no Canada, at some point in the last century we would have invaded for their natural resources. The US also would have pulled a Russia, and taken Japan and parts of Europe, using its rather wild military & resource advantage at the end of WW2.