Generally speaking, multimedia playlists cannot be converted to multimedia files, which means mpl to wmv conversion is not possible. A .mpl file contains just a list of videos or music to be played in a sequence with a media player, not the actual multimedia files. As such, this conversion is impossible.
However, you can manually open the playlist using a text editor and check the location of the actual audio files. If the playlist is not yours, it is unlikely you will find them thought.Open MPL file Open WMV file
Suite of tools for video editing