If everything gets moved to Nashville, take a ride to SFO or SJC to speak to a real live Delta ticket agent in person. (Unfortunately thet NO longer have a local ticket office in Palo Alto T&C by Hobee's) Rescheduling face to face sometimes works better and you may be able to get a reduction on the Nashville tickets.

If you still have the original wedding invites, bring them as corroborating backup.