When American Ballet Theatre performs at the Kennedy Center this week audiences will see a company undergoing one of the most notable transitions in its 75-year history. Three of its biggest stars — Paloma Herrera, Julie Kent and Xiomara Reyes — will retire in the coming months. Together, they embody nearly 70 years of ABT experience. They are all poised for graceful exits; in the interviews below you’ll see that these extraordinary women are outspoken yet at peace with the close of their dancing careers. There is no replacing the veteran ballerinas, as those who know them best can at