Welcome to NeuroTalk:

This is a difficult question.

This is a link to explain the enzyme blocked by this poison:

http://en.wikipedia.org/wiki/Cytochrome_c_oxidase

The resultant damage is mitochondrial in nature.
Here is one thread here explaining mitochondria:
http://neurotalk.psychcentral.com/post657829-1.html

I searched around trying to find the location of the damage possible and this type of poison is just not common and I couldn't find out whether it attacks nerves in the Dorsal Root Ganglion or not.

There is a special MRI that will reveal damage there:
http://neurotalk.psychcentral.com/thread147771.html

Has your husband had a skin punch biopsy yet? To show if neurons in the skin are damaged? I think that should be done too.

When the dorsal root ganglia (which are along the spinal column) are damaged, they may repair themselves...this involves certain proteins that the cells make. Certain people cannot repair either because of genetic inability or overwhelming toxin damage there.

Sodium Azide is toxic to the CNS as well, and that may be contributory.

The supplements used for mitochondrial support are
acetyl Carnitine
CoQ-10
R-lipoic acid (stabilized form)
Biotin (taken opposite to the lipoic --at a different time of day)

We have many posts about these on both the subforum and
regular forum here. You can do a search and find many posts.
This is one thread:
http://neurotalk.psychcentral.com/thread121683.html

One treatment for acute azide poisoning is using a form of B12, called hydroxocobalamin. However, 7 months out, use of this is not mentioned in the medical papers I saw.

One would also need to watch for cellular damage leading to
diabetes, or damaged thyroid gland. So testing for these should be done too. This type of damage would be secondary to the poisoning, affecting other metabolic systems, which may not recover well. Both of these problems cause PN also. It is also possible to uncover a genetic Charcot Marie Tooth problem with the trigger of the poison. There is some evidence that asymptomatic people with this mutation can develop symptoms after a toxin is consumed. The most recent..is Levaquin that appeared in the papers. This link to this is in the "Drugs that may cause neuropathy" thread on the subforum.

I would also suggest using Omega-3 fatty acids, for their anti-inflammatory effects, and their healing actions. Fish oil, 3 a day or Krill oil 2 a day would be a good start.

Also a good magnesium supplement works with the Omega-3's to help nerves heal up.
This is our magnesium thread:
http://neurotalk.psychcentral.com/thread1138.html
(do not choose magnesium oxide--as it is not absorbed from the GI tract).

This would be a start for him. It is important to read here, all about what we have collected for patients with PN. You may find other things on this board, that may be helpful too.