It may not be credible to you. But people refuse them, consciously and willingly, all the time.
You position has boiled down to either (1) Terri can't refuse a feeding tube or (2) I can't believe she would refuse a feeding tube. Neither of those comports with applicable law.
That's not my position at all, I tell you a second time.
My position is that she cannot be deprived of life under the law. The feeding tube is in itself only important in that withdrawing it is the instrument by which she will be deprived of life.