At times I've been autorebooked (VIPRed) while flying over the Atlantic when it was obvious that I was going to miss a connection to AF or KLM. The OP should try to watch the itinerary in flight or check it upon landing. If the flight has go go wifi, one can access the DL website for free; otherwise, you might be able to do this through the inflight entertainment system but I really don't remember how I learned about the rebooking before we landed--I just recall one case when I had a paid business class ticket but was rebooked (VIPRed) into coach and I called the DL DM line upon touchdown.