A bit of a pointless thread this ? I see no in-flight breakups excepting due to gross abuse of the aircraft.
The thing that is most likely to result in the degradation of the structure is corrosion, this is a real problem and it can be addressed by good maintenance practices.
I think that corrosion and the economic situation that had depressed aircraft prices is likely result in aircraft being withdrawn from service as the price of repair exceeds the value the aircraft.