If she is to come to the end of her life soon, she should be afforded the chance to have her parents close by and perhaps her last memories would be ones of them holding and loving her. Perhaps she could hear them say "We love you." Maybe not, but I think that opportunity should be given to her. To stand in the way of giving her some last peace is a very selfish act.
The husband might or might not have had some very valid concerns. But now, he should allow Terri more than the "right" that she at one time, when very young and not knowing the possible consequences, said that she did not want to be kept alive "this way." Friends and family cannot do her any more harm than she has already endured. Let them surround her with love during her last moments on earth. And, maybe, just maybe, she can have a better quality of life than she has now, even if she never recovers, perhaps life can hold a little more than laying, alone, in a hospice room.
Blessings to Terri!
I don't trust her husband. His new squeeze and kids with her has made his guardianship of Terri, biased.