It is important that parts from accident damaged aircraft do not return to the active aircraft supply chain. However not all parts are destroyed every time. I recall that parts of the fuselage of the B747 that ended up in Victoria Harbour in Hong Kong in the 1980s were used as maintenance training aids for engineers at colleges in China.
The engines however were buried in the footings of a new engine overhaul facility in Tseung Kwan O that was being built at the time. A fitting end I would say.