If I understand the injury itself properly, Inky suffered a traumatic injury to the brachial plexus (which is the spot in the shoulder where all the nerves of the arm connect) in addition to the now surgically repaired vascular damage. The most minor thing that an injury to the plexus can do is cause intense discomfort throughout the entire arm and have some weakness. The most major would be the complete separation of the plexus, which would result in total loss of sensation and also motor function loss throughout the entire arm.
The ordinary procedure is to test nerve conduction on an injury such as this...it basically means that they channel electricity through it and see if the nerves are still active (in much the same way that an electrician might check to see if a circuit is complete or if it breaks at a point). This is normally done at the same time as an EMG, which makes sure that the muscle and nerves are operational. BUT, and this is the big one....if there is no nerve conduction detected and the EMG confirms that the muscle is inactive (which results in tissue necrosis), then an amputation is normally done between 72-96 hours later.
The fact that Inky Johnson still has his arm attached to his body (albeit with no voluntary motor function) would most likely indicate that there is still active muscle tissue and that the nerves have been traumatized at the plexus BUT that they still conduct. This is definitely a positive sign, but he is far from out of the woods. Nerve injuries are a complete unknown as to whether or not healing can occur and what can or cannot encourage the healing process. Inky's arm will likely have substantial muscular atrophy; if nerve function were to fully return tomorrow he would still have a very long road ahead of him to recover and return.
Naturally, we all wish him the best of luck for a speedy recovery.