Leonard Rosen was an institution in Northern Virginia, delivering more than 10,000 babies in the course of a four-decade career and offering guidance to thousands of women. He did humanitarian work in Bolivia; he helped develop less-invasive and more-affordable treatments; he offered no-cost treatment to women who could not afford care. But last year, he abruptly retired and closed his practice — a few months before admitting in federal court in Alexandria that he had participated in a fraud scheme by prescribing expensive scar creams in exchange for kickbacks.