How long ago did this take place? How long was he sick? How long has be been in recovery since getting the infusion? My MIL in LTC recovered from Alpha covid May 2020 after basically being on her deathbed. She did bounce back but it took time. She's doing well today. She didn't receive any prescription intervention while she was sick, just Tylenol and oxygen. I don't know anything about the antibody infusion treatment.
I know people much younger than your Dad who weren't yet vaccinated and got alpha covid, myself included. I had it this past March 2021 and still have some lingering issues. Time is the only thing that will make the symptoms *hopefully* go away mostly or completely.
I think you will get more from the forum if you ask more detailed questions about a specific concern - your dad is 89, has lewy body dementia and now is recovering from an illness that causes lingering brain fog in many people, it's going to be hard for anyone to know where one leaves off and another begins.
I know people much younger than your Dad who weren't yet vaccinated and got alpha covid, myself included. I had it this past March 2021 and still have some lingering issues. Time is the only thing that will make the symptoms *hopefully* go away mostly or completely.