>>713150138 (OP)Nintendo keeps the source code for their games, examples are Nintendo giving Square Enix the source code for Seiken Densetsu 3 for the re-release and Ocarina of Time 3d being rebuilt from the source code.
Most Japanese companies at the time destroyed their source code because they put way too much value in that code and didn't want other studios to steal it and use it to figure out how to do what they did.
In the US it really depended, big publishers often had devs delete their source code because the publishers really had no idea what the fuck was even going on so stuff like Fallout is lost, but for smaller studios like say ID, they just released the source code for their games, thanks to having programmers in the management process.