How much of Don Herbert's brain was replaced by spinal fluid? Before we make the comparison, let's make sure that the cases are comparable. A substancial part of Teri's brain died, and was replaced with spinal fluid. This is apparently NOT the situation with Don Herbert.
You do not know that. That was the story created by those who wanted, up-front, to kill her, and those "doctors" like Cranston who want to freely kill everyone who doesn't measure up to their arbitrarily defined "quality of life."
A substantial part of Terri's brain was starved for affection, stimulation and genuine love.
Terri's spirit never died - so her body was forcibly starved to death by a husband, an attorney and a judge.
Before going too far with a theoretical approach on how much brain is required for conscious function, it might be a good idea to review actual findings on the matter.
In the 1960s, before surgical treatment for hydrocephalus, it was possible to observe the behavior of children who lived with as little as 1 centimeter of "cerebral mantle" because of hugely enlarged ventricles filled with spinal fluid. This is the same condition that was referred to in Terri's case as "brain replaced by fluid." It was not possible to tell the capabilities of a child simply from examining the size of the venticles or the thickness of the compressed cerebral cortex.
The idea that you can tell a person's capabilities by looking at a picture of the brain is simply unproved over a wide range of conditions.
If he was diagnosed as PVS he could have been killed in the state of Florida.