User blog comment:IamJakuhoRaikoben/Chapter 373: Life or Death?, Review./@comment-77.194.131.253-20140301094621/@comment-7418318-20140301104418

Future Lucy was knocked out in the collapse of Mercurius Castle when the Dragons arrived and after waking up, she went straight to the Eclipse Gate to travel back in time. Most likely her arm was crushed or severed by falling debris.