Pinnacle doesn't have a pilot crew base in ATL.
http://www.airlinepilotcentral.com/a...onal/Pinnacle/
All of their pilots would need to be moved through ATL and none are available there on reserve. MEM and DTW both have Pinnacle bases so likely they were going to pull someone from reserve, dead-head them to ATL to complete your flight.
I believe the MEM base has closed as well. My understanding is that current Pinnacle bases consist of MSP, DTW, and JFK.