It's something like 3.5 million that Blizzard has lost since Cata. I don't think MoP is able to bring that back. There's always a surge with an expansion, but this time they're facing a current going against them. No matter what, I don't expect another huge loss in the next quarter. It will be 2-3 months after MoP if the trend continues.
People on Legendary think that MoP will attract new players to WoW, but I don't see how that is happening. The features they are adding will not attract people away from the home place of those features. Generally, WoW's adoption of other games features do not attract new players but keep feeding the established Blizzard fan that mostly buys Blizzard games. It's like a Cheesecake Factory menu in that it lists asian food, italian, american and new popular foods, but it's sort of a bland ill-fitting version of each dish. If you don't have a vested interest in it being there then it's just sort of a nice new item on the menu. In that way, it does succeed at satisfying the fans of WoW for who the features are just a nice addition to the back of the box, but I don't see why the people who really love those things would buy WoW to play them.
So the new subs are more likely the addicts coming back rather than new people. Those type of players are also the kind that quit again after a few months.