I don't think I've *mourned* for anyone, really, since my mother died, and that was a long time ago. But my grandma was ready, my MIL had dementia too and a horrible quality of life, and my dad had ceased to be really himself long before he died. It's hard to mourn for someone when their death was, essentially, the best thing for them. A sharp, sudden and unwanted death would have quite a different response.