User blog comment:Kaido King of the Beasts/Chapter 770: All The Fights You Never Wanted to See/@comment-74.179.166.126-20141212190608/@comment-3075024-20141212224833

Applying common understanding of how Ope Ope works .. cutting and attaching body parts is part of its ability .. all there is left to see is if Law can re-attach his arm that was cut by someone else. BUT, Law has medical background, has fixed Jinbe and Luffy who were poked inside-out and has done limb attachment on Punk Hazard between men and animals so I think the loss of arm is temporary.