Can we survive the death of the nation-state?
That was your opening question. The answer depends upon who you include in your "we."
There have been many diruptions in the past: plaugues, wars, famines, more wars, colonialism, and slavery. Some people always survive and thrive, many people don't. Many of the people who do, don't care about those who don't.
We are not in a slow decline now, we are in rapid, thrity year drop. I feel that in the next two to four years, we will know if the US has caught hold of the last branch and pulled itself out, or if we will become the next Poland, then Russia, and then India.