I think part of the problem regarding the 'value of life' is whether we are looking for an objective or subjective answer (that's the perennial conflict in medical ethics). Subjectively, the value of life is wherever we place it - no one can step in an arbitrarily decide for someone else what the quality of their life is. In the case of Terri (and many others like her), we go by the best evidence we have available. The ideal is substituted judgment - in which one person knows the patient well enough to make choices based on the patient's values, as if they were the patient him/herself. At the other end of the spectrum is the best interest standard, in which choices are made solely on what is in the patient's best medical interests. Most situations like this fall somewhere between the two. Objective value of life is very difficult - for one, what do we measure it with, and what are the units?