This ship has sailed = este barco ha zarpado, este barco ya ha zarpado. Puede utilizarse en sentido literal o como una metáfora para indicar que algo ya se fue o que se perdió una oportunidad.
This is a sad and sore topic for me. Ten years ago The Simpsons was one of the best shows on all of television. It was witty, original, sarcastic, silly and most importantly funny. Now however the show is dull and at its best is only good. Unfortunately I think the ship has sailed for The Simpsons, and although they haven't 'jumped the shark' they sure did let the show sink into obscurity.