When artists have unreleased tracks that leak, what law is keeping people from re-recording it and calling it their own?

Is it because it is property of the record label?

Also, what is keeping people from covering the unreleased material or do the same laws apply here as with released songs, regardless of whether or not the original artist is not losing any profit because he or she (or s/he as the hipster english teachers prefer) is not selling his or her version.

For example, let's say that Timbaland and Justin timberlake want to record another album, but their lack of talent is keeping it from happening. If they covered the songs from "Box of Chocolates" (and gave the appropriate to credits to everyone that was involved with the original), what would Prince or Warner Brothers (idk which owns the rights to his music from that time period) sue them for? Royalties, maybe?

What if Justin Timberlake, b/c he seems like a sly bastard, released the cover album with a magazine or something so that no one is paying money for the cd itself?

Would Prince (or Warner Brothers?) be able to stop it from being released, or would he just receive a large majority of the royalties?

(some of these questions may seem contradicting, but i am just trying to give examples that cover all the possibilities)

I'm not trolling or trying to sound smug, just curious about these issues and do not know anyone that is informed enough about the music industry to ask.