Board Thread:Naruto Discussions/@comment-26210090-20150315213729/@comment-5273810-20150315214653

While Guy losing the use of his leg is sad, I do believe it can simply be explained as something like both the chakra networks and circulatory systems in the leg were severed meaning that replacing it with a zetsu leg or Hashirama cells would ultimately be useless. That's at least how I rationalize it.