Like with any game engine, it is possible to use tools to extract game data from the PCK file. Even if this was impossible somehow, tools that inject in the game process and intercept graphics API calls could still extract textures and 3D models.
However, from a legal standpoint, doing so does not grant you the right to use the models and textures elsewhere. If there is no license attached to your work, then people aren't allowed to do anything with it (to the extent permitted by law).
