The fact that the tube is already in place does not change the answer because there is no ethical difference between withholding and withdrawing life-support. In order to determine whether the gastrostomy tube is effective or ineffective, we must ask why it was implanted. Certainly it was not implanted to keep Nancy Beth in a persistent vegetative state. The present condition of Nancy Beth makes it clear that the tube in question is ineffective. But in an ethical evaluation of burden to a patient, the consideration has never been limited to physical pain.
Psychic pain is also to be considered as well as the burden to a family.
The whole purpose of making decisions for people who are incapable of making decisions is to make sure they are treated humanely as worthwhile human beings. People find psychic pain just as much a burden as physical pain. People across the country attest that they would want care withdrawn if it only prolongs existence in a totally debilitated state. Moreover, loving people consider their families when they make decisions about the burden of medical treatment. Proxies should do the same.