Conscious death and integrating the mind with the psychic being are rare even for those whose mental faculties are intact during death.
Dementia however affects only the surface mind which in many if not most people enters a state of disorientation and confusion a few hours to a couple of days before death. The real thing is the inner being, the inner mind that is important and its state during death depends upon the kind of life one has lived. I have seen number of people who had Dementia but departed in a beatific inner state full of the psychic glow. What matters is the development of the inner being rather than the outer personality that is anyways dropped off during death.
Affectionately,
Alok Da
