It would be perilous for JW organization to advance a figurative view of the 144,000. What happens to their view of two classes and the enormous focus on paradise earth? What about the mountainous criticism of the churches of Christendom heralding heaven as the hope? JW's exclusive and literal take on the faithful and discreet slave is based on the view that the heavenly class is different from the great crowd.
Making the 144k figurative doesn't mean they'd suddenly have to believe everyone is going to heaven. They would keep their two-class system, and just put heavy emphasis on the 144,000 evidently meaning the number of Christians with a heavenly hope would be a very small subset in contrast with the "great crowd".
The concept of paradise earth is one of the most appealing aspects of the Witnesses to the majority of those who sign up. Thus, you'd still have the vast majority holding to that hope. The percentage of partakers would definitely spike, no question. But I think it would stabilize rather quickly. Probably no more than 5%, quite likely less than that.