Board Thread:Spoilers!/@comment-26225812-20150618081046/@comment-1894786-20150707001240

It doesn't have to be a literal death. It could be a figurative permanent death, like the Rumplestiltskin the Dark One dying while Rumple Gold lives on.

Also, the Dark Swan does exist in literature since JMo said in an interview that she's been doing research on black swans in literature. They're probably more of a symbolic character rather than any one identifiable character from a specific story, however.