With the closing of “Phantom of the Opera,” and his latest musical, “Bad Cinderella,” there is no Andrew Lloyd Webber production on Broadway for the first time in 43 years. The composer who helped define musical theater over the past half-century talks with correspondent Seth Doane about theater’s future; the problem with the Tony Awards; writing music for Britain’s new king; and the death of his son, Grammy-nominated composer Nicholas Lloyd Webber.