ANSWER: Jesus said “many,” so that means a significant number. If history is any indication we can look back to the turmoil that engulfed the Society back during the First World War. And back then “many,” in fact a majority, of Bible Students left the organization when Rutherford took it in a new direction.
But this time it will be different. At the coming of Christ JW’s will be required to abandon the Society altogether. (‘Let the man on the housetop not come down…’) That will be a huge test of faith. But we can be confident a great crowd will pass the test.
It is no coincidence that periodically the Watchtower reinforces the notion that it will be the source of life-saving instructions at some point in the future. But ask yourself, is it reasonable that after having perpetrated a fraud on trusting Christians regarding the invisible presence of Christ since 1914 that Christ would use the Society in the future to announce his real presence or to publish life-saving instructions of any kind?
It is my position that the blowing of the first four trumpets of Revelation that bring woe upon a third of the sun, a third of the moon, etc, that turn a third of the waters into wormwood, symbolize God’s judgment of the organization. And the thirds represent a minority, but nonetheless sizable number of persons, who will be adversely affected by God’s curse.