Persons will 'leave' only when the organization know as Jehovah's Witnesses ceases to exist.
Even after 1975, dispite the allusion that an exit of many left the 'truth, most stayed 'loyal to the faith'. Suggestions of hundreds or thousands leaving the organization is probably correct, but from a percentage aspect very few threw in the towel and left.
Some did become inactive for a while but many returned after some years ... to wait on jehovah.
Some that became inactive after 1975 left for good in the early eighties after learning about Ray Franz's story. But in reality, most of us might have heard a general retelling of those events but never knew of any details - the Time magazine expose and interview was banned as apostate propaganda.