The one thing that keeps the majority of JW's in is FEAR. Fear of a number of things, sometimes all of the things we could list, sometimes just one or two.
The fear that keeps PIMO folks in is the fear of losing Family. Remove that fear, or diminish it greatly, and PIMO's would leave in droves.
If a Court Action were successful in a major Court that the JW Org shunning was illegal, and they could be sued for damages, they would have a sudden shaft of New Light and change the Policy. I know they have foreseen this, and structured things in such a way that they think the Org itself is immune from Legal action, but if they are wrong, and it happens, I think the dwindling of the Org from their Reported 8 Mill plus would happen very fast, until they were down in the hundreds of thousands only.