Press release linked below. Delta only has 18 777's, and clearly they think the need for long-range wide-body aircraft will stay depressed long enough that they can get by with their other aircraft types and (eventually) taking new deliveries. This also does not bode well for their view of the near to mid-term future of international travel loads in general.
I understand the economics of it; newer aircraft types are more efficient. But I'm sad to see this--the 777 in general is one of my favorite aircraft, and Delta had resisted the urge to shove in an extra seat in each row of the Main Cabin. This meant they were some of the most comfortable economy seats left flying.