If the flt is diverted to BNA, there may be crew as well as fuel issues. At best you eventually get to ATL for an overnight but I learned the hard way last wk that all Priority service shuts down at ATL at 11 pm.

If you don't mind a long wait, there is 24-hr service down by baggage claim but I can tell you from experience, there is no love for Elites after 11 pm. Once I got to the counter, the individual was very kind and accommodating given the circumstances.