I highly doubt the Poly will be going anywhere. I could see Disney doing some pretty significant refurbs (say, on the scale of what the Disneyland Hotel is currently going through), perhaps stripping down and rebuilding the Grand Ceremonial Hall, rearranging portions of the lobby interior, redoing the pool, or converting some of the wings over to DVC. However, Disney has shown recently that they do honor authentic-looking, short-scale buildings even when temptation demands otherwise (building only a 5-story Grand Floridian DVC when we all know a tower would have sold just as well), so I doubt we'll see any 10+ story monstrosities built on the site of the Poly. I think its time is due for some major refurbishment work, which every resort needs at some point, but I'm sure Disney knows not to demo or radically modify one of its most popular resorts.