I cannot believe that a person with dementia who hits someone commits a sin! I was nursing a lady with a terminal condition of Alzheimer’s Disease (who also was a diabetic). Every time I tried to give her the necessary dose of Insulin (via injection) she would hit, bite & kick. Yet, when she went to meals, she was quite lucid. The last time I took care of her, this 4’7" lady THREW me across the room into the edge of the door jamb by grabbing my lab coat. I had a crushed tibia (just one year after having my patella- kneecap to laypersons- fractured.) The leg never healed properly, and I was forced into retirement. Did I blame her? Was I angry at her? Of course not!!! She didn’t realize what she was doing, and the behavior change was due to her disease, not intent.
As for receiving the Sacraments, I had a personal experience with this and not a good one. My Aunt died of advanced Dementia. When she was nearing the end, the only word she could say to any comment or question was “no”, with a lovely smile! When I read prayers or Scripture to her, she would smile, close her eyes and be very quiet and calm. I asked my priest to allow me to take the Blessed Sacrament to her (I was a Homebound Minister of the Eucharist then) and he said “no one with dementia can receive the Sacraments!” I was a long time forgiving that Priest, since my Aunt died a week later, and the Priest came to the burial service and blessed her coffin, but would not come to see her that last week or administer ANY Sacraments. My Aunt was not violent, and would consume anything put into her mouth. She seemed to follow or at least understand Scripture, even though she couldn’t speak. If a person can swallow, and does not spit out the Holy Eucharist, I think it should be administered to them as long as possible, especially when it is obvious the end is near. Certainly he could at least have administered the Anointing!