The States existed as individual nations before they bonded together and formed a 'confederation' under the Articles of Confederation. The first confederation did not work in a way that pleased everyone, so they followed up that arrangement by forming the Union under the Constitution. Before it became effective, it had to be approved by the individual States. The present Union began in 1787, whereas the States existed prior to that. When England made peace, it was with each State/Nation on an individual basis.
I suspect that if the union does not work out, that the States would continue some cooperative relationship with each other. The nature of the relationship would likely be some type of alliance, since there is so much overlapping history and culture. They would also develop some trade agreements where preferential treatment is given to former members of the Union.
As to whether we would be better off or worse, I don't know. What I do know is that there would be less involvement in wars that do not directly affect the States. That in itself tells me that there would be fewer tragic deaths. There would be less debt, and the United States would not be the world's policeman. So if fewer debts, fewer wars and more trade are important, we would be better off.