The "world" of Christianity is getting closer and closer to realizing that SCIENCE is right and that all religion is wrong. There will be a tipping point in the distant future where that solidifies into something important. Tipping points don't necessarily remove the minority who were "wrong." Watchtower and it's former members will continue to be insignificant to the "world."
I do understand what I think you are asking. It's something like "When will Christianity realize that Jehovah's Witnesses are a dangerous high-control group and not a part of mainstream Christianity?" All Christian sects are strange and far from the truth of science, in my opinion. It doesn't really matter how many from a strange belief system out of line with science realize that Jehovah's Witnesses are too strange for the title of "mainstream." The importance will be when the scales are in favor of science instead of religion.