Here is what I found. In the manual, pg. 4-57 is the description of the functions of the music box. There is no mention about transferring music. It does however mention, that if the hard drive does need replacement due to a malfunction that all data will be erased. I was thinking that if you bought another Infiniti perhaps they could just move the hard drive into the new car if was similiar. I think the 08 is a 9.3 gig, the newer models may be larger.
You can delete the music, I am sure if you traded in or sold vehicle, they would want to be able to start with a clean hard drive. Pictures below:
