Complex sentence: When Stark refused to fire Lennart, Robbins resigned, to be replaced by Bob Fosse who got the relatively little known Barbra Streisand to play the leading part in her very first movie.
Split into simpler sentences: When Stark refused to fire Lennart, Robbins resigned, to be replaced by Bob Fosse. Fosse chose Barbra Streisand to play the leading part in her very first movie.