Regarding your point about dementia, I think this may be a challenge with translation. By awareness, I don’t think Dharmakirti is referring to cognitive faculties, such as memory or correct discernment. Rather, I understand this awareness to mean the mind’s basic capacity to apprehend an object. For example, somebody who has severe dementia might have trouble remembering things, but if you placed an apple in front of them they would still be able to see it (given their eyesight wasn’t impaired). Similarly, if you pricked their finger, they would still feel pain. So regardless of the condition of the body, that basic capacity of the mind to apprehend an object is never diminished.
Even the mind of somebody who is hallucinating still apprehends the hallucination. Similarly, if all our sense faculties go dormant the mind is still able to apprehend mental objects, so that fundamental knowing quality of the mind is always there.
Not sure if that makes sense?