Engines are overhauled, with many parts replaced with new items.
Manufacturers are required to provide product support for many years after aircraft go out of production. Typically 25 years although this may be longer if there are still customers for their services.
A lot of aircraft are "Parted out" (Scrapped) and the useable components may be overhauled or repaired and sold on for further use. This is where accurate aircraft records are important so that the hours flown and flight cycles of parts is known.
A former employer bought several Lockheed Electras and Airbus A300s to strip for spares to support the operational fleet.
Hope this helps.