Shan't - the forgotten contraction

The word shan't went the way of the dodo bird when the word shall began to fade into the background. In years past, we were taught that "shall" went with first person, but second and third person required "will." Thus, "I shall, you will, he will." However, that rule has pretty much gone by the wayside, and "will" is used universally, while "shall" might occasionally be used for emphasis, but only then.