You're defining "society" as a pointless philosophical abstraction. I'm defining "society" in terms of the only thing I care about: the people and country around me. I'm not interested in the history books that remain to be written. I think most Americans feel similarly. It might be satisfying in some intellectual sense if "the worldwide shared culture of the 21st century" (of which America might represent a small fraction numerically, but which is disproportionately American in its composition) survives, but does little good for Americans who suffer.
The country/government is irrelevant, the people are the society and that is what I am defining it as. Governments have come and gone with great frequency; societies almost always survive them. Really only genocides, cultural or otherwise, can halt them (and mad bombers are in no position to perform any sort of genocide against modern society).
It strikes me as a fairly American-centric viewpoint that conflates American government and American society. Plenty of other countries with strong, long-lived, cultural identities have gone through numerous governments in past centuries, many of these governments lasting a few short decades or less. A government is much easier to kill than a society, and dies with far fewer consequences.
If the death of a society is not what you are actually concerned about, then perhaps you should have put some thought into your initial comment before drawing comparisons to the fall of the roman empire. If merely the fall of governments and economies is what you are worried about, there are countless better examples.