I thought there was a surgery where you can add a small electrode to part of the brain in a effort to shock out the seizure impulses. I understand I'm probably not saying this right
In my opinion it is because the hemispherectomy does not target certain life sustaining rehions such as brainstem and thalamus based on surgical precision and anatomical imaging preventing the neurosurgeon from damaging these key life sustaining regions. So they likely survive ig.