Hi OP,
Sorry you are going through this.
1. Keep him working as long as possible. His paycheck will be significantly bigger than monies on SSDI. Work will keep the brain active. I would not say anything to his workplace. Bruce Willis kept working for years even after he was diagnosed with cognitive decline to support his family.
2. Early 40's is very young for this. He needs good docs due to his age.
3. Consider moving closer to his parents or your parents or other family for supports.
4. Figure out how you can get by on one income (yours)
5. Make sure all of his POA's are in order.
6. Is he on any meds? Have docs/pharmacists take a look at all of his meds. Many cause memory issues.
PPI's are a big one. You are only supposed to be on these for 8 weeks. Long term use is linked to causing memory issues. Talk to his docs about getting him off meds linked to cognitive decline.
7. Does he drink alcohol? Get him off of alcohol. It is linked to memory issues.
8. Get this book from the library
https://www.amazon.com/End-Alzheimers-Program-Prevent-Cognitive/dp/0735216207
9. You might consider getting an appointment with a functional medicine doc/MD in addition to his regular docs.
10. Make sure he is drinking a lot of water. Our brains need water.
11. Ditch sodas and other sugary products.
12. Eating unprocessed foods and no sugar got Mom around a 30% improvement in brain power.