If someone wishes NOT to be kept alive, and for their family not to endure 15 years of life-sustaining care, it is cruel to them to keep them alive, whether they know it is happening or not.
Sophistry will get you nowhere.
Well, since she was capable at some point during the past 15 years of responding, someone should have just ASKED HER if she wanted to die! If she could open her eyes upon request, as shown in this video, http://web.tampabay.rr.com/ccb/videos/Terri_Big_Eyes.rm, she could certainly answer a yes or no question and SPEAK FOR HERSELF rather than rely on her estranged husband who had taken up with another woman to decide.