WHY NOT ?
To extract a orphan .rar file which is in continuation of a series of rar files which finally extracts to a valid file/app/games/movies/songs/etc,
just right click on that particular .rar file 2 bring up the context menu
There u get the "Extract files........." option",Click on that 2 get the "Extraction Path & Options Menu"....where u get the option of "Keep Broken Files" under the General tab". Click/activate that option & finally Click on OK 2 get ur extraction of that particular partially downloaded file!
C the Scrrenie below:
Hopefully do as told & U will get finally what u need!