I read carefully your question and I am so sorry.
I think that after 5 years possibility to treat is low but first of all he should do another new spine MRI
and than to consult with neurosurgical if he may do anastomosis
roots (but you should know that is very dificult).
About disco-osteophytic flatting the dural is mechanic traumatic displacement that damages spinal medula and nerve roots.
So you may help him with sport activities like swimming.
Wishing you and your cousin all best.