during An Lushan rebellion. if you have born and lived as a citizen of the greatest nation in the world for as much as your life, you won't call it quit easily when your nation is in trouble. Just like many Tang citizens who fought hard to preserve the empire, there will be many citizens who fought hard to preserve the US empire.

I do think that it is possible for the US to break apart though. The Americans are very individualistic, and very state centric. They consider federal gov a necessary evil. If the US is no longer the richest country or the strongest country in the world, coupled with political polarization, economic depression, and racial segregation/discrimination, there is a big chance the US will never recover from this. But the great empire can only fall from within.