His diet & lifestyle will be of primal importance in neurodegeneration. Majority of the evidence suggests that repair of central nervous damage is extremely difficult but it may be possible over some time. Know thou that if there was tissue necrosis, those area may permanently be destroyed. The brain is however extremely plastic and may find ways around the scar tissue. 
It is important that your husbands remain active. Daily. Physical activity stimulates brain-derived neurotrophic factor (BDNF) in the same way that lifting weights helps to grow muscle. It helps the brain rewire itself. 
Make sure his motoric abilities are challenged and tested. Take different walks, ask him to stand on one leg, close eyes and balance. Dance with him, challenge him to try things like yoga (if his health allows it), explore new interesting ways to get your cerebellum (coordination centre) engaged. 
Create mental challenges, play scrabble, chess, logic games, cards. Talk to him, show him photos of old times, make him remember very hard. Thse areas can come to life again. Stimulates his senses with known smells, tastes and revisit places. Discourage him from consuming social media and looking at screens but do promote visual & mental training of any kind. Even snakes & ladders or ludo is great. 
Secondly, he needs to have his vitamin D checked & optimised, that one is extremely important for neuromodulation. 
Zinc is another one, a key component for neuroplasticity 
Adequate protein in the diet but make sure it comes mostly from plant sources. 
Adequate fibre is essential. For example research on Parkinson's patients show that the greatest destruction in the region of the brain called Substantia Nigra (responsible for dopamine production) atrophied the most in patients with lowest fibre diets. 
Make sure his diet contains lots of green leafy vegetables & wholegrains. He needs sources of B vitamins & magnesium to support cerebral ATP production. 
Green Tea appears to be able to aid neuroplasticity to some degree and some may herbs like Gotu Kola and Gingko as they stimulate microcirculation in the brain capillaries.
He may benefit from supplements like: phosphatidylserine, phosphatidylinositol, gotu kola, lion's mane, Coq10 for mitochondrial regeneration, 
And finally, I'd encourage you to maybe look up a book specifically on this topic. On neuromodulation, neuroplasticity. Perhaps something from Joe Dispenza.
Definitely worth finding a specialist in post-traumatic neurodegeneration though, they will know much more. 
All the best!!
 
EDIT: the most obvious also, make sure you guys get on the top of why the aneurysm happened. COmmon causes are high aortic pressure in the brain and atherosclerosis as well as arterial stiffening. If his blood pressure is over 120/80 you need to get that under control as well as if his LDL cholesterol is high. There are many natural ways to do that, plant based diet being the most effective. 
Have his blood sugar tested (HbA1C) that can contribute to arterial damage as well. 
 
 

Hey
We asked our GP to prescribe Provigil for my hubby.  He declined.  He said that it is for narcolepsy and he looked for information that it is also a cognitive enhancer and said not only could he not find any, but that he had not enough knowledge on the subject so could  not prescribe it.  He also said it is a stimulant.  Now it may well stimulate the brain but there is no amphetamine effect.  Unlike other times, I did not attempt to push the issue feeling it would be a totally fruitless exercise.  We have ordered elsewhere.  I'm extremely wary of its effect so there's lots of research for me to do in the meantime.  If anyone has any advice on the subject I would sure welcome it, as to be honest, I'm a little scared - and feel that I probably need to be to do this absolutely properly for him.