It seems to me that duty has more to do with collectivist feeling in general than nationalist feeling specifically (which is just one subtype of collectivist feeling). You have duty if you belong to and care about something larger than yourself. I think what's weakened people's sense of duty is the wave after wave of increasing individualism that probably accelerated some time after WWII, and has been going on for as long as I've been alive. A big part of duty is sacrificing your individual interests for another, which has always been hard but is even harder if social attitudes don't give it much support.
I can imagine that having a tangible cultural impact, particularly around our sense of collective ownership and duty.
For example, you shouldn't litter, and if you see someone else doing it, you have to overcome your shyness and point out to the kids their duty. And if you get busted littering, you should feel bad.
The thing that happens when authority breaks down is everything else is questioned too, whether or not that authority had anything to do with creating the pre-existing norms.
The collapse of authority and the establishment, yes. But Duty wasn't imposed by an authority. There's a quote that I can't find at the moment with the effect of "no-one can tell you your duty, it's something you must discover for yourself".
totally agree that it's metastable. Which is why I found it fascinating with the Shame connection - shame appears to be metastable too