I was auto-rebooked while in the air on a ATL-NRT flight - paid D1 - two years ago that made me miss my connecting flight to HKG. I was very disappointed with what DL did to me and was fortunate to find a sympathetic agent to correct faulty assumptions made by DL.
BTW, I knew before leaving ATL that I would mis-connect and thought I had settled everything with the DM phone line but the frustrating changes happened during the actual flight.