if Mark composed some music in the typical film-score-music style (like the last exit to Brooklyn, Princess Bride, keyboards-sax-celtic tunes on Local Hero, etc...), of course it can be well performed by other musicians.
But if he composed some guitar-oriented tunes, don't you think it would be weird if it would be played by another guitarist than himself ?
Or does it mean that in this case, the music would be aired on stage as a playback, while actors/singers would sing live along ?