How gruesome do we want to get?
Time flies like an arrow; Fruit flies like a banana. - Groucho
Why is this so hard to understand?
The primary function of our [all] species is to procreate. We develop all kinds of ways to facilitate that primary function and to keep our offspring alive and healthy so it doesn't make a lick of sense to unhook the woman as long as leaving her hooked up has a reasonable possibility of producing a healthy baby.
Say you have two patients, one brain dead with healthy kidneys, and the other saveable with a new kidney. If patient one is not an organ donor, you can't take his kidney even to save the other. It's about consent, even if you assume that they might want to be a donor in that situation. You are assuming that she would want to be kept alive until the baby is born, but you have a legally binding piece of paper in your hand that says "no life support." She didn't consent to this, and you're happy to assume that she would.
The rest of us tho...we will continue to fight for our rights and what is left of hers.