At that point you have two options: conciliate with the baddies or arm yourself. Including nuclear weapons- even Japan is rethinking it's stance on nuclear proliferation. This is nothing new really Europe was a war torn continent for a thousand years.
In 1000 years, if the US gets taken over, the new power that takes over will have the same reasons to keep the peasants doing what they are doing to keep the state useful as a whole at the time of the takeover. If a completely different nation state takes power openly, sure, a few idiots who have been too brainwashed to serve their old exploiters will struggle... but they'll eventually be forced to get in line or suffer. This will not affect the population at large. They'll keep doing whatever they are doing, like they have been, for many many generations all over the world. New history will make old history boring and uninteresting to the politically minded, but it will be just the same for everyone else.
The outcomes will be vastly different if it happens in the next couple of hundred years though. There is no way there will be enough decentralised resources for people to survive by themselves... so the elites losing the power will try to do everything to hold on to it. They will control food supply to starve the people and force them into war... and won't stop until a lot of damage is done on the population.