Han Solo is right. You fly whatever aircraft you can make the most money on. If I had two houses for rent, one paid off that earned 3000 a month cash flow and another with a mortgage that earned 2000 a month cash flow, and I can only have one tenant, am I going to let the paid off house sit empty or the mortgaged house?

The reason md88s will be parked is because of higher operating costs due to fuel/mx, not because of how the debt is structured.