They can't go back for a lot of the current generation of Witnesses. At the convention they clearly said: There is no room for another world power, this is the last world power, there will be none after that.
Once China has established itself (maybe after the Great Cyberwar that's brewing) and starts running the show, there will be no more room for the Watchtower. The US is broke and has hollowed itself out so it's on the verge of economic collapse which is inevitable.
The problem the Watchtower has is that things are simply moving too fast. They can't keep up with the developments in this world since things are at a tipping point. They came and preached right after the last tipping point smoothed out (the fall of the British Empire and an establishment of a chaotic amalgam of nations that could fit any so-called prophecy in the Bible).