When brain cells die there is generally no bacterial decomposition. The dead brain cells are liquefied and digested by other cells and the empty spaces in the head are filled with liquid.
I knew a child who suffered prenatal strokes and there were large parts of his brain just not there any more, but since he was so young he did very well - normal intelligence, delayed motor function but normalizing by seven.
“Brain death” is different from some parts of the brain bein dead or dying - it refers to no brain waves, no brain reflexes, no breathing reflex.
If there WAS bacterial decomposition, there wouldn’t be these arguments and lawsuits. Death would be rapid and indisputable - cardiac death too. Bacterial meningitis is a fast killer.
Decomposition does not necessarily have to occur through bacterial action. As a medical researcher, I have studied cell death in a sterile environment. Dead cells break down in various ways, depending on the type of cell death that occurred. With the type of death I suspect has occurred, I would think that the cell membranes would disintegrate and organelles would lose their structural integrity, releasing enzymes that digest cellular biomolecules. I will refrain from describing any further, out of respect for people's sensibilities. I am very curious to know what is actually happening, if breakdown products from a dead organ can penetrate into the circulatory system and so forth. I am also curious as to how long a semblance of life can be maintained in a dead body. Yes, I know this is morbid (but I'm a scientist).
I have read about young children who have had half of their brains removed because of a seizure disorder. They seem to do fine with half a brain... although I wonder if some sort of prosthetic is stuffed into their skull to keep the remaining half in place. The plasticity of a young brain is truly amazing.
By definition of some here my relative with ALZ... judging from scans of her brain should be dead.