The US abandoning its imperial position would accelerate its collapse because American hegemony and prosperity is dependent on its imperial reach. In the event of the empire entering a death spiral it would launch a renewed offensive of military adventurism to maintain its position and rally around the flag at home.

This isn't like the end of the British Empire where it was able to pass the torch of world hegemony to an extremely agreeable and friendly regime. The only alternatives to American imperial hegemony in this moment are China, which is completely unacceptable to the white, Western world, or a renewed European bloc imperialism that has yet to truly emerge.

Right now the strategy to head off an acceleration of intra-capitalist competition and internal instability is to ignite a new Cold War with China. But China is in a much stronger economic position than the USSR ever was at any time in its history. And moreover, the suicide of the USSR was a ludicrously unlikely event in the first place. Three decades of rampant and misplaced Cold War triumphalism have potentially fatally infected the American imperial mindset. The American political and economic elite legitimately believe American capitalist triumph is foreordained and they can win a second Cold War against a stronger rival. But a more likely outcome is the extermination of humanity through nuclear war that preempts a climate apocalypse.