If you can somehow get past the conceptual problems with secession, you must still confront a series of difficult practical issues. How do you divide the family silver? What happens to the nation’s debts? In particular, what do you do with the armed forces and entitlement trust funds?
Debts could be shared either on the basis of population or GDP. Public lands would be returned to the states. The military would present serious questions, however, as a disproportionate number of bases and personnel come from the RSA. Some of those assets would have to be transferred to the USA. How that would work, I have no idea.
The RSA states, for the most part, are net beneficiaries from government transfers. If entitlement trust funds were divided on the basis of GDP, the new RSA programs would go broke very quickly, and major cuts would be required. That is less of a problem than you might think, however. The leaders of the RSA would eagerly embrace the concept of a tiny welfare state dominated by the wishes of the white and wealthy. The USA would aspire to be Denmark; the RSA would use Central American banana republics as a template.