Unbeknownst to even the doctor (this was before ultrasound), the woman was carrying co-joined twins. A head was delivered, and the woman labored long and hard, and nothing else presented.
They finally called in x-ray--and saw what the problem was. It was really gruesome, but they decapitated the presented head, so that they could do a C-section. and save the mother. Needless to say, the other twin was dead, too.
Of course, this was an extremely rare situation, and in this day and age, would be dicovered long before delivery, so the doctors would be prepared to do an immediate section when the woman went into labor.
Most people on either side of this issue don't talk about this much, but I believe that a very large number of partial-birth abortions are conducted because of serious fetal abnormalities that cause the parents to want to terminate the pregnancy.
I feel terrible for anyone who is in a position where they even feel the need to consider PBA. It's a brutal and sickening procedure, and I can't imagine the guilt someone would feel after doing it.
Having said that, your example though an extreme case, makes me think that there is some merit to including a reasonable exception where the life of the mother is at risk. Nothing like the gaping holes that Diane Feinstein and others have tried to include, however.