I agree with OTWO, they will spin it to give the impression that it means the end is near.
I am reading a book about cognitive dissonance. They have found that the more people have invested their time/money/emotions into a cause the less likely they are to be discouraged by negative information about that cause, in fact it is the reverse, they often become even more convinced.
They gave an example of a woman who predicted the world's end on a particular date. The most faithful went to her house to wait for the end with her. When the world did not end she had a new revelation that their faithfulness caused God to delay the end. Those who waited in their own home eventually drifted away from the group. The most faithful, those who waited with her became even more devoted followers.
Sound familiar? Just like the bible students who believed Christ would return in 1914. When that didnt happen, instead of admitting they backed the wrong cause, many readily accepted the ridiculous "invisible return" explanation. It's just human nature to believe what makes us feel most comfortable, nobody wants to think they were wrong. It happens with cops when they zero in on the wrong suspect. They tend to ignore evidence that exonerated the suspect, sometimes even DNA evidence.
That's why falling numbers will not be a problem for the Watchtower, increases prove God is with them, decreases prove the end is near.