They can run them 30+ years. Airframes are holding up VERY well. No need for capex expenditures when the cab use cash flow to pay down debt. DL has proven to the industry that the airframes last much longer than initially thought and in the case of the 772, UA is showing that the 772 is a beast! with a retrofit this will serve AA well (And its debt load)

plus, I believe new frames from the OEMs are years out.