> The code is also copyrighted and owning a license for a game does not make you safe from being sued for pirating that game or its code. It's fine in this case only because the engine was open sourced.

Nothing makes you safe from getting sued.

See also: [1]. You could also reverse engineer in a solid jurisdiction.

I ran C&C Generals in Wine on Linux back in the days. More stable than Windows XP.

[1] https://en.wikipedia.org/wiki/Clean-room_design