The brain is an unusual organ. There is evidence that it can sometimes adapt to work around damage. As an example of the brain's ability to adapt, consider a surgical procedure sometimes used for extreme seizures called Functional Hemispherectomy (emphasis added)

Twenty to 30 years ago, hemispherectomy involved removing half of the brain completely. However, early enthusiasm for this operation was replaced by skepticism due to progressive neurologic deficits caused by superficial cerebral hemosiderosis. This complication most likely was due to small recurrent hemorrhages into the large surgical cavity associated with minor trauma and from lack of support for the remaining hemisphere. To limit the area of removal, multi-lobar resections, subtotal hemispherectomies and hemisphercortisectomies were performed instead. Although these procedures reduced the superficial hemosiderosis, they resulted in less seizure control, probably because seizures continue to arise from residual portions of the damaged hemisphere. To duplicate the good results of the complete hemispherectomy while avoiding cerebral hemosiderosis, several modifications have been devised. Currently the most common operation performed is the functional hemispherectomy. In this operation, the temporal lobe is removed, corpus callosotomy is performed, and the frontal and occipital lobes are disconnected. The blood supply to the remaining brain is left intact; hence, the skull remains filled on the side of the operation rather than being left with a large cavity.

Imagine - literally having half of your brain removed. For most patients, motor control is regained within a matter of weeks. Some MRI images are shown here.

Some people suffer seeming limited brain damage but the results are devastating. Others suffer what appears to be massive damage but suffer minimal ill effects. Here's a good summary source comparing the different imaging techniques when it comes to evaluating brain trauma.

If you're really interested in the science of evaluating brain trauma, you can go to sources like this:

Packard RC, Ham LP: Promising techniques in the assessment of mild head injury. Seminars in Neurology 14(1):74-83, 1994.

Abstract: Closed head injury may result in varying degrees of brain injury, from slight to severe and irreversible. Severe or even moderate head injuries often result in obvious structural damage, which is usually easily detected by imaging or neurophysiologic assessment. Mild head injuries (MHI; defined by Rimel et al.1 as a period of unconsciousness less than 20 minutes, a Glasgow Coma Scale of 13 or greater, a negative neurologic examination, and a duration of posttraumatic amnesia less than 48 hours) are typically more subtle. In spite of persisting symptomatology, there is typically no anatomic evidence of injury as traditionally assessed.2,3 (See Young and Silberstein in this issue of Seminars). A variety of distressing symptoms often follow MHI or neck injury. The most common are headache, dizziness, impaired concentration, memory difficulties, fatigue, irritability, depression, and anxiety.2-5 Paradoxically, individuals sustaining MHI often have more intense posttraumatic symptoms than those who sustain more severe head injuries.3 The persistence of these symptoms often results in feelings of distrust from the public, the legal profession, insurance companies, and even other physicians.4,6 Even in the face of legitimate posttraumatic symptoms, patients may still be labeled as "accident neurosis," "personality disorder," or "malingering in order to receive compensation." New technologic advances in experimental head injury and neuro-imaging techniques have revealed that even MHIs result in subtle changes in the structure and physiology of the brain.7,8 Such cerebral alterations may explain the persistence of memory difficulties, depression, distractibility, dizziness, and headache. Traditional studies, however, including radiographs, electroencephalography (EEG), computerized tomography (CT), and magnetic resonance imaging (MRI) are often normal in MHI. Transcranial Doppler (TCD), positron emission tomography (PET), single photon emission computerized tomography (SPECT), and quantitative analysis of EEG and evoked potentials (brain mapping) have only recently become available for clinical use. These new and promising techniques will be reviewed in detail in this article.

Food and water are necessities for all human life. A lot of people have difficulty swallowing, be it caused by brain injury, throat trauma, birth defects, or other reasons. A person on a feeding tube is no more on life support than a baby who depends on a bottle. It's a far cry from someone on a respirator full time, or a heart/lung machine, or even dialysis. If it's your opinion that people who aren't able to feed themselves are somehow living lives not worth living, then there's no point ever talking to you again.