Misunderstanding may arise by confusing the Buddhist and scientific definitions of death. Within the scientific system you spoke quite validly of the death of the brain and the death of heart. Different parts of the body can die separately. However, in the Buddhist system, the word death is not used in that way. You'd never speak of the death of a particular part of the body, but rather of the death of an entire person. When people say that a certain person died, we don't ask, "Well, which part died?"
(The real brahmin is the one who:) ... has crossed beyond duality ...knows no this shore, other shore, or both ...(is) settled in mind ... without inflowing thoughts ...is without attachment ...endures undisturbed criticism, ill-treatment and bonds, (and is) strong in patience ...(is) without anger, devout, upright, free from craving, disciplined and in his last body ...has experienced the end of his suffering here in this life, who has set down the burden, freed!
I have the True Dharma Eye, the Marvelous Mind of Nirvana, the True Form of the Formless, and the Subtle Dharma Gate, independent of words and transmitted beyond doctrine. This I have entrusted to Mahakashyapa.
Let yourself be open and life will be easier. A spoon of salt in a glass of water makes the water undrinkable. A spoon of salt in a lake is almost unnoticed.