I cannot speak directly to your situation, but, my wife and I had tickets on DELTA ticket stock, FTE (Calafate) to EZE on Aerolineas Argentinas then connecting to ATL on DELTA.

At the last minute, Aerolineas decided to fly the EZE flight to AEP instead (for unknown reasons) and I knew I was going to be hosed.

Surprisingly, DELTA (really their handling agent) was really easy to deal with once I arrived at EZE and rescheduled me for the next day without question.