Nina is retiring at the end of NEXT season, not this one.
I know nothing regarding julie retiring, but I would imagine it isn't the case. She is one of the longest lasting ABT principals and is married to Victor Barbee (associate artistic director) so if she was indeed retiring, I'm SURE the company would make an event of it.
I knew about Ananiashvili's retirement next season, but I would swear that the subscription brochure mentioned that the last Giselle of the company's 2008 Met season would be Kent's farewell performance. It was the reason I bought that series. I'm fond of Kent, having watched her perform over the past 20 years in a variety of roles.