Ok, so your definition of life is whether a person can recover from a certain amount of brain damage. If I understand your assertion correctly, after a certain amount of unrecoverable brain damage it isn't possible to kill them because they are, according to your definition, not actually alive, or, in other words, they are already dead and we are merely sustaining the remainder of their body.
That's a unique and so far as I can tell substantially different
definition of death compared to most of the medical community. For us to have a reasonable conversation about this topic I suspect you would have to help me understand what what "too much" and "recover" mean in an objective, measurable sense. Perhaps you are referring to a
persistent vegetative state, which is measurably different from brain death. It may well be that you don't think detaching them from their life support system(s) would kill them, from your point of mental privilege it can be hard to see what kind of "life" they might have. However I think we can fall back to a legal standard here to determine whether detaching someone from life support is killing them or not. Hypothetically, if a doctor detached life support for such an individual they have no connection with, without permission, would they not be charged with murder or manslaughter?
Please understand that I'm restricting myself to a discussion of the legal aspects of the laws being put in place to enable physician assisted death, healthcare, and interrelated aspects and how these, coming together, may have unintended consequences (ie, slippery slope). So while a discussion of the morality of killing (and mercy killing, and suicide) as well as opinions of what constitutes life, and the specifics of this case in particular are interesting, I'm primarily concerned with what the law says, and how it's actually implemented.