I like to think that the reason Prince wasn't interested in a will is because he knew "you can't take it with you", and that he knew after his passing, what happened to his worldly goods was not as important to him as the kingdom he would inherit. We all know how deeply spiritual Prince was. As he sang in "Way Back Home", "I was born with this dream, this dream outside my head", meaning the physical world that we take as reality is only a dream, and all he was doing was waiting until he could find his way back home again. What happens after his passing to his wealth, to his catlogue, to everything he had acquired on earth, was just not important to him.