The only problem I see with them taking Everest down once Avatar opens is that you are going to see a HUGE increase in Guests and they will need something to do. Animal Kingdom is generally the park Guests will give up a day of their vaca at to go somewhere else. With all of these Guests now returning for Avatar you want them to truly see that the park is a full day park now and that it has a nice selection of rides. In my opinion, Everest should go down before Avatar opens. Fix the yeti and any other effects that needs fixin', give it a nice sprucing up wherever it needs it and then open it up just before Avatar is open to the public. With the addition of ROL, the nighttime entertainment as well as the night safaris, the park should be able to lose Everest for a few months and still be ok.