When musicians know they're about to die, they seldom produce their greatest work. But there are exceptions, including the late Cincinnati Pops conductor Erich Kunzel, jazz saxophonist Stan Getz, and composer Dmitri Shostakovich. We explore the phenomenon with Wall Street Journal drama critic Terry Teachout and Crystal Zevon, widow of the late rocker Warren Zevon and author of a biography about her husband, I'll Sleep When I'm Dead.