I believe there are plenty of people in comatose states, who breathe on their own, yet are fed by feeding tubes.
I visited my sister's MIL in a nursing home in the early 90's.
She was on a vent, but was otherwise fine. Sitting up in bed, writing to communicate.
There were 3 other woman in her room and all of them were on feeding tubes, and asleep. Not a tube like Terri's. These were nasal tubes, that you could see.
I asked my nurse friend why were they all being fed this way, and she said because they're understaffed and don't have enough time to feed these people by mouth.
I don't know if that was really the case, but it was an eye opener.
I now know, that an NG tube is put in only on a temporary basis, and then they go to the stomach tube.
Prayers for Terri and that they feed her soon.