The parents argue that she would want to stay alive. I don't see why the husband's word should carry any more weight even if the law says it should. (I'm not saying they should ignore the law. My point is that the current law should be changed).
I don't know if the parents should let it go or not. But since they are the ones who are caring for her and are her parents, I don't see why they shouldn't be given some say in this matter.
Taking out the feeding tube will starve her to death. They aren't sure if she will die in a few weeks or a few days from this. If she supposedly is suffering in her state, why is starving her to death the solution. She is not having the breathing done for her. She simply just can't swallow or eat herself. That's it. There are a lot of people who have this same problem.
That being said, if the parents were okay with her being killed, then I'd be okay with it as well. But since they are providing the care and want to keep her alive, I side with them.
For what it's worth, I think Noonan's piece on the subject is worth a read. If you are pretty adamently on the husband's side I doubt you'd want to however.