I suspect like most situations like it before it in history, it will take a collapse and rebuilding to "fix". I think it can limp along dying for a very long time though.
The authour John Michael Greer talks about this a lot. The collapse of a civilisation is something which takes centuries. It's not overnight, and it's not linear. It's a process where there's a drop in level of complexity and reach, a plateau for a while with lots of talk of rebuilding and maybe even a small amount of growth - but never to the previous level - and then another drop, and so on.
The collapse takes place because of resources and systems. A potential empire is a country which has X% of the world's population, but more than X% of the world's resources. It uses those resources to make a better lifestyle for its populace. Humans being what they are, the imperial citizens demand even more, and of course the neighbours want some, too, and so the empire devotes some of its resources to expanding and getting even more resources.
Of course, the use of the military to acquire more resources and defend the resources the empire already has, has a point of diminishing returns. With the effective return on their military investment declining, the elites may get panicky and start hoarding. This causes internal tumult as the citizens demand more. To manage the distribution of resources, and all the military, the empire puts in place systems. The citizens now see these systems as another way to distribute the resources. "If I can't improve my life by farming," (for example) "I can do it by becoming a Farm Inspector."
Now, some systems add value, and these will be put in place fairly quickly. Roads and road-mending, for example. But as the obviously-useful systems have all been put into place, people will start putting in systems with diminishing returns. It's exactly as it is with the military.
So again: an empire is a country which has X% of the world's population, but much more than X% of its resources, and wants even more. Over time they develop a military also in excess of X%, and bureaucratic systems to handle it all. And both the military and systems eventually have diminishing returns - and in the end,
negative returns. Spending more resources on them makes the empire
worse off.
When the pie is getting bigger, anyone who wants a bigger slice can get one. When the pie is getting smaller, the only way to get a bigger slice is to take it off someone else. Indeed, even to keep the same sized slice might require taking it off someone else. And so in a declining empire we see more and more internal conflicts.
As I said, this process takes time. A person can be happily walking around in the capital of a great empire, and then in 50-75 years' time their grandchildren can be in that same empire which is now rather diminished, its streets no longer as clean and its palaces less numerous, and
their grandchildren are using the old palace stones to build sheep fences, and only know old tales of glory by word of mouth.
We sometimes think of the "six degrees of separation" thing, about how I know someone who knows someone who - and thus indirectly know everyone on the planet by just a few steps. We rarely think of it vertically, through history. Think of Queen Elizabeth II. Her first Prime Minister as Queen was Winston Churchill. When he was first elected to parliament, Queen Victoria was on the throne. And Victoria was born in 1818. By just two degrees of separation, Elizabeth II knows someone born in 1818.
Now if the Scots and Irish have their way, there may in the next few years no longer be a United Kingdom. And so with just a couple of degrees of separation in history, we see Britain going from being the largest empire on the globe, to - perhaps - no longer even having a united homeland. A fall in living standards will of course inevitably follow this, and there will be internal tumult as people fight over what's left. One of the good things about democracy is that it gives people a way to fight over resources and power without the legions marching.
Twitter fights are the modern day version of the old church doctrinal disputes. They pretend it's over philosophy of living, but really it's just a status shuffle, a fight over a diminishing pool of resources. The longer they're doing that, the more we put off actual fighting. Long may it continue.
But this is what's happening.