User blog comment:B214/Question and Answers/@comment-74.110.105.73-20131010152504/@comment-9339850-20131010160158

Well Issei lost his whole body once, and the boosted gear stayed in his soul with Ddraig holding it together, so the Boosted Gear is probably more attached to his soul and not his body. but even so, if he did lose his arm either Azazel or Doctors in the underworld would be able to either construct or attach his old arm