I have a niece who overdosed on cocaine and alcohol over the summer - she had seizures and went unconscious several times, and then had to be placed in a medical coma for a couple of days because of brain swelling. Alcohol was the prime factor in the brain swelling.
After rehab, she had a myriad of issues with memory (short term and long term) , in addition to quite a bit of anger and frustration. The anger was due to having to actually manage her life for the first time in a while without her little helpers (drugs and alcohol), and the confusions and memory issues certainly added to the frustration. She went through some stages of depression.
Her neurologist (after several scans) found no permanent damage but likened it to a concussion - although no blunt force trauma occurred, the damage done by the excessive drinking, which caused the seizure, gave her the same symptoms. In her circumstance, no permanent damage had been done, but it will take a while to unfog her mind.
I would also second the neuro-psychiatrist consultation. Honestly, it's not going to do you a bit of good to second-guess and diagnose by google, and it certainly won't win you any favor with the medical staff already treating him. If your husband is content with the treatment, and the staff is as well, you'll just continue to make enemies by pushing anything right now.
I'm not trying to be insulting at all so please do not take it that way, because we all tend to do this, but what you are currently researching is a rare form of a rare degenerative disease. Early-onset is pretty rare, and FTD is the most rare form of early onset alzheimers/dementia. If you are suggesting to a medical staff that a very rare disease could be the culprit, they're going to write you off.
Just document what you can, and simply hand over your observations for the time being. It's what you can do at this point. If you feel you can suggest to your husband to simply get a second opinion to ease your mind, then perhaps work on that angle as well.