[breakingcups]

That depends on how much time you're willing to invest. The recently DMCA'd re3 project is a full decompilation of Grand Theft Auto 3 and Vice City, through a clever combination of all released versions (eg. the Android version leaked some symbols, Renderware signatures were somewhat recognizable on PC and PS2), pre-existing community knowledge (The mission script format had already been reversed which provided many clues by looking at its interpreter, many memory addresses were known by the modding community, etc.) and just a massive collective effort, it fully reversed the cpp game that is Grand Theft Auto 3 (and VC).