Complex sentence: Boortz announced his retirement from radio on June 4,2012; his last live show aired live nationally January 18,2013, with Boortz's regular fill-in host, Herman Cain, replaced him on January 21,2013.
Split into simpler sentences: Boortz announced his retirement from radio on June 4,2012. His last live show aired live nationally January 18,2013.