O'Connor is gone. Retired and gone.
It didn't happen as far as I know. She agreed to stay until her replacement takes over. There isn't one nominated to take her place now that Roberts is the nominee for CJ. She will be around till she is replaced. If she had changed her mind and retired immediately it would have been all over the news.
So, who is O'Connor's replacement? It seems to me that Roberts is now Rehnquist's replacement. (BTW, it is so sad that Rehnquist didn't get the chance to swear in his old clerk. I am convinced he didn't retire just so he could do this.) Certainly if O'Connor retires before two confirmations, there is still a vacancy.