At around 15 years old an A320 won't have much useful life left in it for passenger operators and there is no afterlife as a freighter like there is for the B767/757.
Fuel burn will be well above the current sharklet and neo versions, and dispatch reliability heads down hill which isn't acceptable to low cost operators with tight scheduling.
This basically limits options to parting it out or selling it to an airline in the Congo who keep flying it until it crashes into a village at the end of the runway whilst taking off grossly overloaded.