"The engine continued to operate normally and the aircraft, an Airbus 320, landed safely," the statement reads. "Safety is our top priority at Frontier Airlines and we would like to acknowledge the professionalism of our pilots and flight attendants. We are working to get our passengers to their destinations as quickly as possible.”
The engine may well have been turning but I doubt the thrust wasn't affected. Exhaust nozzles are carefully crafted to make the most of the engine's power.
The assymetric drag must have been horrendous. Kudos to the crew getting it down safe. Final approach and flare must have been tricky with changinging attitude.
Edit: I thought one could not latch the fan cowls with the c ducts unlatched. Certainly on the bigger fan engines there is a large red handle that hangs down when un latched making it impossible to close the fan cowls. Its that long since I've opened an A320's c duct.