Are there unique economic benefits to countries vs trade blocs?

In My Humble Opinion
1

In a fictional world where outrage over Trump causes the 50 United States to secede and subdivide into 3-4 regional sovereigns – somehow, miraculously avoiding a civil war in the process and maintaining a trade alliance with each other – what do the new regions stand to lose with regards to economic benefits of the prior Union?

If the new Uncomfortably Close States of America enter into a trade bloc modeled after the EU, NAFTA, APEC, etc., would they be nonetheless severely weakened in terms of international agreements, tariffs (both internal and outside the bloc), etc.? Would the bloc see greater risks from being intertied with the economically weaker regions, assuming no shared currency?

Would there be expected benefits to the increased sovereignty and rule-making within the new countries that the former behemoth of a union made too large and difficult to manage?

What about its anticipable effects on the new citizenry, at the day-to-day level of inflation, taxation, market stability, etc.?

2

The biggest risk would be that one of the new countries passes laws harmful to its economy or has a bad central bank. The other worry is that decreased mobility between states would harm tourism and prevent people moving from depressed areas to growing ones.
The upside is that smaller countries are usually better governed, and the depending on the configuration of the new countries they might be able to have monetary policies better attuned to their economies.