Music, in particular, can reach places in folks who are losing their language, especially old favorites. Other sensory experiences, like favorite foods, flowers, are good as well, along with just talking, reading, etc. Reality orientation isn't usually helpful and can't be retained (ie, the fact that they are dying, etc.) but focusing on expressions of love, gratiitude, and caring can get through. Though, I agree with myvonne that saying it's okay to leave is a lovely act of compassion.
I was a geriatric mental health consultant in a past life, and these are common questions. It sounds like you are doing a wonderful job just by showing your love.
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