Board Thread:Questions and Answers/@comment-67.142.183.24-20130618213018/@comment-26324183-20150419172021

Echo did survive because Dave Filoni had a sketch of echo being a prototype arc trooper. Link: http://media.moddb.com/images/groups/1/5/4477/echo_returns_variations_clone_wars_season_7_by_engelha5t-d7c1x7u.jpg