So, so sorry for your loss.
Alzheimer's is such a terrible disease.
We lost my dad to it three years ago when he was 75 y/o. It was like losing him twice. He hadn't known us for several years and hadn't spoken for months before he died. I was so hoping for a miracle that last day, hoping that he would look at, recognize and speak to my mom one last time. It didn't happen though. She went to that nursing home every Mon, Wed, Fri, and Sun for at least two hours for three years, trying to get him recognize her and to just let him know she was there. They were married over 50 y/rs. It's been three years and she's still not over his death. It's gotten easier though. At least you were able to take care of your mom at home and made her last days happy. We tried, but my dad got obsessed with starting fires and wandering off, so we had no choice but to put him in a nursing home. We hated to do it, because he had always said that he'd rather be dead than in a nursing home, but after repeatedly trying to set their house on fire and managing to get out of a locked house, there was no choice. I was really worried about how my eldest son, (who is the oldest grandchild and was definitley my dad's favorite), would handle it, but he made the comment that we had really lost Papa years ago when he didn't know us anymore and that he knew he was happier and better off where he is now. I hate that only my eldest grand daughter will remember him (the other GKs were too young when he died) , but no matter how much I miss him, I wouldn't call him back, even if I could. At least not in the shape he was in. I know he's much happier now.
My husband's dad died just last month when he was 92 y/o from heart problems. My husband was an only child, was especially close to his dad, and took it really, really hard. I had to remind him that his dad had lived a very long and productive life and wanted to go. The night before he died, he said he was ready to go. Unlike my dad who hadn't known us in years because of the alzheimer's, his dad's mind was sharp right up until the morning he died. My F-I-L was a very special, well loved man who will be missed, but lived a very full life, so had no regrets. We as their kids hate to let them go however, no matter how old they are or what shape they are in.