Lehman, Merrills and the Fall of the Roman Empire: The Geopolitical View

Bear Stearns, Fannie Mae and Freddie Mac, Lehman Brothers and Merrill Lynch, and perhaps even AIG.  The Great and the Powerful of US capitalism are falling like dominoes.  Who is next?  Will the US Government be forced to rescue new institutions that threaten to collapse?  The likes of Lehman and Merrill Lynch are unlikely to hit the man on the street, but certainly not AIG, Citigroup or Bank of America - the latter has now assumed the unknown toxic assets of Merrill Lynch on its balance sheet.  The man on the street will cry blood if their life savings in AIG, Citigroup and BOA disappear overnight.
How about the USD itself? 
They all say that the USD is unlikely to collapse given that the biggest hoarders of US T-bills and Government bonds are SWFs and national reserve custodians of Asian and Middle Eastern countries.  But if US companies keep collapsing and if the US Government begins to print money to save their companies, it will take one SWF to blink and press the sell button, and all the rest would dump their USD, and that at any price.  Then we see all collapse like a house of cards.
When that happens, we would see perhaps the next Great Depression.  In the long timeline of history, the greater impact is not the economic calamity and human hardship per se, but the decline and collapse of the American Empire, an event of dramatic geopolitical significance. 
Predators are already sniffing around...Russian stretching its muscles in Georgia and landing its warplanes in Venezuela; Venezuela, Bolivia and Nicaragua - all formerly banana republics in the American backyard - have expelled their US ambassadors.  Now - let's see what China, Iran and all the other regional competitors of the US would do next.  Does this not remind one of how the Roman Empire fell?
I am not sure the fall of the American Empire, for all its idealism and contributions to human development (notwithstanding disasters in Vietnam and Iraq), is a good thing for human civilization.  But History and Time are cruel, and the world has seen the rise and fall of countless empires when they over-stretch economically, militarily and politically.
We will see.