You are right! Not long ago the entire world used the British Sterling (obviously the United States didn't exist back then). If the British Empire could lose their dominance in just a couple of centuries, than of course any empire could.
Most people don't know that USA has puppet states/colonies all over the world - not only the main country, but literally everywhere. They control more of the world than any other state has since the beginning of time. USA is the most dominant, largest empire in world history.
British empire is within the last 100 years, within living memory of a few people. Its not quite ancient history.
Here we are before ww1:
The difference with USA today is the system is political not an empire or even the remnants of one. Its voluntary that USA has a base in Qatar and also Saudi Arabia and Japan too. And that Japan holds a trillion in US debt while possibly going broke in its own government debt and budget is just a maybe, nobody can force them to continue in support USA and they may not even be able. Japan is a democratic country and even Qatar and the Saud cant guarantee they'll always continue in support. The idea that USA somehow can force any of those countries or even more ridiculously invade is not even on the table. So its not an empire, its a long standing economic system which to me clearly does favour USA a bit too much and is likely to change in future.
If all the British commonwealth countries (roughly shown above) still held Sterling as their domestic currency that'd be about equivalent. UK doesnt control any of those territories and it would have to be a beneficial system for them to continue to do that.
Whats most likely from here is the US dollar is replaced not by bitcoin or gold or another country but another political system. A halfway, the best suggestion I heard was the SDR or the paper of IMF bank which is linked to UN and supported in theory by every country of the world.
They even included China I believe. I think Russia and China would prefer some system based closer to gold, both are major buyers but I dont know. The bottom line is bitcoin is part of the change away from old paper to maybe new paper or another system, it isnt likely to fail due to one country in decline suffering from its own debt.
None of that relates to bitcoin, if anything bitcoin relies on China for its system of value as most mining and purchasing is done there? China is fixed to dollar by its government and bitcoin is unfixed, if dollar fails it will still leave Chinese citizens wanting to use global markets away from their own government.
I do hope bitcoin does not mimic the tricks and failings of paper but allows fair usage by every country of the world to do honest trade. If bitcoin is part of a capitalist system it will improve the situation of every user and I do not see it failing vs the ending of a biased paper system with many flaws, there is no fixed link in that way.