Marissa Mayer is basically an ex-CEO walking at this point. As "bad" as it sounds, the only thing that has kept her around recently is her pregnancy. No board would want to step into the mess of letting a woman CEO go during pregnant or immediately following pregnancy and maternity, no matter horrible her performance. You are right, I give it about 6 months before there's an announcement of her departure for whatever reason, probably "spending time with the family".

As it has been put by others, Mayer will hold the title in corporate history as the most expensive CEO for a very long time.