Complex sentence: Once completed, it will be the largest ship flying an Italian flag and will replace Costa Fascinosa as Costa Crociere's flagship, and replace the Costa Concordia which sank in 2012.
Split into simpler sentences: Once completed, it will be the largest ship flying an Italian flag. It will replace Costa Fascinosa as Costa Crociere's flagship, and replace the Costa Concordia which sank in 2012.