I’m not quite sure this is The Man vs. the Starving Artist. Mike Batt’s biography seems to indicate he’s quite successful. In fact, barring calamitous financial management I’d bet he’s loaded.
I don’t think there are many broad lessons here. According to this article
The only lesson I see is that you shouldn’t list another person as a co-author of your work unless you want to pay them some royalties.
Hell, my first argument in such a case would be that Cage’s copyright is invalid because copyright doesn’t vest until a creative work is “fixed”, or recorded in some tangible, perceptible medium. Silence, being by definition the lack of sound, cannot be thusly fixed.