N0m: Do you imagine that the Shulchan Aruch codified a Halacha (that is cited throughout the Rishonim and as you pointed out is based on the Mishna and Gemora) that is some exceptionally rare circumstance that is virtually inconceivable to transpire in accordance with the described Halachic description?
That asked, think about the Titanic and how the crew triaged who to rescue and who not to, because there wasn’t enough room on the boats offloading passengers. As you know the crew triaged based on gender. So much so, that Congress actually held public hearings on why some prominent men were permitted to have their lives saved by giving them the limited space on the life boats when there were still women who weren’t given that slot. Congress was angry that those men were saved before the women.
N0m, of course Yidden who follow Halacha would have done it oppositely of the triaged gender based decisions of the Titanic crew, based upon the Halacha we are discussing. But my primary point in bringing the example of the Titanic is that, no, it isn’t as rare as you seem to be making it out. And, yes, there are times when this Halacha would kick in.