Mythical daughter, opponent no longer with us (8)
I believe the answer is:
Here is my best explanation:
'mythical daughter' is the definition.
'opponent no longer with us' is the subsidiary indication.
'opponent' becomes 'anti'.
'no longer with us' becomes 'gone'.
(Other definitions for antigone that I've seen before include "The Burial at Thebes is Heaney's translation of Sophocle's (8)", "Tragedy by Sophocles", "tragedy", "Greek drama", "Greek play", "Tragic heroine", "Make drama", "Jocasta's daughter" and "classical play".)