Duncan Sheik, composer and songwriter, died on September 19 at 56, leaving behind a body of work that traced an uncommon arc — from the radio ubiquity of 'Barely Breathing' to the raw theatrical power of 'Spring Awakening.' His was a life defined by deliberate reinvention, by the willingness to trade commercial comfort for the harder, more collaborative demands of the stage. In choosing the less certain path, he gave a generation of performers and theatergoers something more durable than a hit: a work that changed what they believed theater could hold.