It seems you are using decline of an empire as a stand in for societal decay/unrest. The two often go together, but it is not required that they always do.
In my view the most likely of the negative outcomes is that US slide into a hybrid regime (democracy/authoritarian) with a less likely negative outcome is into a full authoritarian regime. If that happens, there are two ways I see that it can go. The first is the one that grabs all the headlines, Nazi Germany. The second, and in IMO more likely of the two, is one where elections happen, but change nothing; other than that daily life is pretty much unchanged people still go to work, newspapers are still published, there is still some political dissent, people still earn a wage, and people still buy things.
On the positive side, I see the most likely outcome as holding the current status quo for an extended period of time. With the less likely case being a marked improvement by implementing at least some of the reforms mwulff mentioned.
For someone in their adult years today and living a good and/or privileged life, I expect the chances are good that they will continue to do so for the rest of their life.
In my view, many people talking about/planning to or actually leaving the US, are exercising a luxury, in that they have the resources to pick where they want to live and the skills/funds to be attractive to those places. To be clear I am not passing judgment on the decision to do so, just acknowledging that is it much easier to move to your first choice when you have money and skills/degrees/certification that are in demand than say a general laborer with minimal credentials.
In that light, to me the real questions are 1) Does the US align with my values/represent who I am? 2) If no, do I want to fight to try to change that?