How does a funeral for spouse effect an Alzheimer's patient?

My MIL had dementia (and cancer) when she attended FIL visitation and funeral. At the visitation she was upset each time she saw FIL in the casket. I don’t think she was any more upset than any other spouse would have been. She did forget each time almost immediately. She was in a wheelchair and we tried to keep her away but she was drawn to the casket.
She really enjoyed seeing family members and we were glad she was there. The next day at the funeral she did fine. At the cemetery when taps were played, she stood and saluted the flag. It was very sad for all of us. No one could believe she stood. It was amazing really.
After the service there was a luncheon and she seemed to really enjoy that. She died a month and a day after FIL. No one regretted her being there.
Following days she did not ask about him. She seemed to know he was gone.
It was the last gathering before her own funeral.

A few months ago one of my DH aunts nephews died. Aunt (93) has dementia. I did not take her to the funeral but I did take her to the luncheon afterwards. It was a success for her and the family.

I also took her to the funeral home before guests were to arrive. I’ve done this on two occasions with her. She didn’t want to go to the funeral but wanted to say goodbye. She would also forget. She would ask me if someone in the family had died.

I think it’s hard to make a blanket statement on if it’s too upsetting for them. It’s an individual situation. I would be prepared to take them home if it proved to be a mistake. My SIL and I took care of MIL in order for her children to be free to visit with other attendees.
My husband helped me with his aunt. So it was fine.
We took comfort in them being with us in our grief.

When my mom died I did not take dad to her service. He would have been very confused and have to be reminded every few minutes what was going on. Absolutely no point in putting him through that.

It really depends on the stage they are in. Early stage maybe aware what is going on. Later on may forget they have a spouse. If your asking tryjng to determine if a spouse should be present, it really depends where they are in their journey. I would keep a funeral as simple as possible. Maybe just friends and family. A viewing would be too long. My Mom only lasted an hour before she was ready to go home. I may have graveside service just family and very close friends. Maybe a nice lunch. If a big luncheon be ready to take the spouse home after a short time. They don't last long and like the familiarity of "home".

Grieving. If early stages they may grieve. Once they are told though, don't tell them again. If they ask where their spouse is, tell a little white lie. Their loss of short-term does not allow them to retain the info their spouse is gone. Telling them over and over that spouse has died will only put them thru the grieving again.