You just tackled a very difficult issue and presented it well. I liked it. I actually live with my grandmother who has late-stage dementia, and has had for some time, as she's has the disease for about 10 years. It's really heartbreaking watching someone go though that when you live with them (though unlike Severus, my grandmother never really spoke at any length about it happening, though she knew - we still find random paper about the house where she was trying to write down family members birthdays and such)... I could feel for Harry in this story, and his family, especially when I realized Harry was losing his mind as well. I liked how this highlights some of the seriousness of dementia (forgetfulness, wandering) but didn't dwell too much on really bad stuff (such as dangerous mood swings, inability to recognize loved ones, incontinence, being unable to string two words together...) you showed that through it all there are still good days, good moments... you ended it at a good point, I really liked the plant talking they had going on there and how Harry was able to see Albus.