Complex sentence: By then, quartet singing was fading as a commercial phenomenon, and Broadnax retired from touring, though he did continue to record occasionally with the Blind Boys into the 70s and 80s.
Split into simpler sentences: By then, quartet singing was fading in commercial viability, and Broadnax retired from touring. In retirement, Broadnax continued to record new material occasionally with the Blind Boys into the 70s and 80s.