I don't think Art can exist without an Artist, but I'm using the word 'Artist' fairly loosely. I would call a piece written by John Cage using results of chance Art, because he conciously chose to take these random results, convert them into another form, and show it to others. Similarly I would call music created by converting statistics about the Earth's orbit Art because someone had chosen to use the statistics that way, although, not being religious, I wouldn't call the Earth's orbit itself Art.
So I guess I would consider anything that has been deliberately created to be seen (although not used) by others as Art. Although possibly not good Art...
So, following on from this, I would see a piece of music written to imitate another style as Art in it's own right.