If you ever end up in a persistent vegetative state, it's grueling for your family & loved ones. We now have the tech to keep you sort-of alive for many years, but it's not cheap, of course.
There have been ridiculous controversies in the US (see http://en.wikipedia.org/wiki/Terri_Schiavo_case for a good example) about families that have decided (with the support of medical professionals) to pull the plug after years of suffering... and there may be protests from the devout (because to some people, any action or explicit inaction that causes a life to end is murder), political interference all the way up to high levels, etc..
It's also somewhat sad that if it's time to give up on restoring a person to working order, the ways of doing that may be limited to somewhat slow & cruel methods (like removing a feeding tube) rather than more humane methods, due to the legal terrain.
There's a certain level of brain damage from which it's not possible to recover a functional person; it's hard to draw that line (see OP for emphasis on that), but it's a line that people in real life are obligated to draw on a regular basis.
If you make a living will that specifies that you do not wish to be kept on life support if your brain activity is below X for Y time (a bit of research required here), you can save the people you leave behind a great deal of heartache by not foisting the decision on them.