As far as I know there is nothing "official" from Disney stating this is happening anytime soon. I may be wrong. I know they've hinted at it, but I dont think they've set a date. In fact, just so you know, the CM's at POTC in March 2002 said it was going to go down very soon, but they then moved it back. The CM said that they were going to do extensive refurb on the cave (now there's talk of even bigger stuff, on down the "river"). If you've ever seen pictures of the "roofing" of the cave, taken by flash camera, around the area before the "drop", there are many holes in the ceiling due to aging.
The "rumors" are that it will go down at the end of this summer, but don't count on anything until you hear it listed as an official refurb. At this point, if Disney hasn't announced it, I wouldnt' count on it yet.