Kanye West, one of the most popular, influential and commercially successful musicians of the past 20 years, is currently without a record label or a publisher. Universal Music’s Def Jam Recordings and Sony Music Publishing have parted ways with him, like many of his other business partners, in the wake of his recent behavior and especially his wave of anti-Semitic comments. On purely music-business terms, the situation is unprecedented. Def Jam, which owns the copyright to his recordings up to sometime in the mid-2010s and distributed subsequent releases up to last year’s “Donda” album, has confirmed that his deal with...