I would be more inclined to think anywhere between 10% and 25% no more.So many older Jw`s have invested so many years in this religion with time and money and their participation in it , they are not going anywhere
.Pride is also keeping a lot of people in.And so is self esteem ,how many want to admit they have been duped all these years and then admit its just not true.? Not many
And i think it is surprising how many leave the religion over the years yet the religion never leaves them and something happens in the world or their life and they jump straight back into the religion.
Not only have they never made the "truth" their own they have never proved to themselves that the JW religion is anything but the truth.
They are what I would call the LAZY believers usually born ins who drop in and out over many years actually fence sitters . ,those that the bible identifies as those who are like corks tossed about by the seas not knowing what they believe and accepting whatever their Elder tells them.
Thats why I say between 10% and 25% but definetely no more.