I don't think this is unknowable; just a couple minutes of Googling turned up a bunch of studies. Consumer Reports posted an analysis from journal articles indicating that maternal mortality from C sections is strongly correlated with specific hospitals; since the predicates for an emergency C section generally aren't correlated, that strongly suggests it's the procedure and not the circumstances that are to blame. The major causes of mortality due to C section include sepsis and anaesthesia errors (this happened to my wife during the birth of our first kid), which are also intrinsic to the surgery and not to the circumstances of the pregnancy.