Until pilot training issues become a cost issue, DL should, from an economic view, keep these birds running. Honestly, I'm wondering if they retired the -40s prematurely only b/c of the 'marketing' of old aircraft. We hear pilots love them - real aircraft - and they are rock solid (if gas guzzlers, but also free). As a longstanding customer, and yes a D-diamond, I wish they stayed on as long as possible.