Chicago will welcome back Rachel Schur in the role of “Roxie Hart” and will welcome to the cell block for the first time Nik Walker as “Billy Flynn” beginning Monday, May 4 at the Ambassador Theatre. With a book by Fred Ebb and Bob Fosse, music by John Kander and lyrics by Fred Ebb, Chicago is now the #1 longest-running American musical in Broadway history. The current cast of Chicago features Whitney L…