When people talk about the Fall of the American Empire, they are usually analogizing the state of American now (we've been doing this from about 1950) to the state of the Roman Empire at some point in the 400s. In fact, most people's knowledge of that period tends to be murky at best, but what they mean is the end of a powerful and dominant empire, and its replacement by something else. This will happen to us in the near future, they say...ignoring how long it actually took the western Empire to collapse, and the Eastern Empire to retrench and restructure.
But I don't see a collapse of that sort as a near-term possibility. The Rome I fear we are actually like is that of the 1st century BCE: the late Republic. That Rome remained strong on the periphery, and collapsed in the center through vicious infighting through what was once called the Roman Revolution. The old ramshackle republican system was replaced by a military dictatorship where "the image of a free constitution was preserved with decent reverence". That collapse doesn't have the clean (if misleading) visuals of barbarians streaming through the gates, and so doesn't get used as journalistic shorthand for what we face.
Interestingly, our fiction is more cognizant of the resemblance than our journalism. Colleen McCullough's "First Man in Rome" series, Robert Harris's Cicero novels, Steven Saylor's Gordianus the Finder mysteries, and the TV series Rome have all been popular, and speak of the corruption and downfall that characterized the period.
Was the Roman Revolution inevitable? Did the Republic have to end? Was the price paid for the Republic's dissolution a good one? Many citizens, cut off from public participation in any event, certainly must have thought the price was more than fair, giving them prosperity and personal security.
The growing deadlock of our own representative republic, with its gargantuan yet petty squabbles over self-inflicted wounds like absurd healthcare financing structures, unsustainable entitlement programs, and increasingly untouchable public sector employees, certainly seems bound for some tour de force "solution" that will lead to a state none of us expect, or want.
Reading about the pompous Marius, the sinister Sulla, the smart-then-surprisingly-dumb Pompey won't provide any kind of specific guide to our era, though it's fascinating. But it's important to see how choices can get made by default, how people can put exaggerated faith in institutions that don't maintain themselves without work, and how a loss of freedom can be greeted with relief by a people who don't see themselves as giving anything important up.