The music itself or the playlist? I've seen iTunes corrupt its playlist, but the physical music files always remain. Don't get me wrong, it is still a huge pain in the butt, and one of the reasons I uploaded all of my music to Google Music and got an All Access subscription.
I had the underlying files deleted - 1-2 songs missing from what used to be a full album, and iTunes' XML index still had references to the files. This was several years ago, long enough that I don't remember what the iTunes version numbers.
