"When a Witness dies (if I'm correct), he or she immediately becomes teachable."
Can you cite scripture that teaches this? If not, what is the basis for your belief?
I'm not certain I understand what you mean.
Once a Jehovah's Witness dies, I assume they will experience what everyone else experiences. In short, they will realize that they are still "alive" in the spirit. Many have had near death experiences where they see their own bodies and are greeted by dead relatives. At that point I would assume that they will now realize the doctrine that they "expire" at death is an erroneous doctrine.
The Jehovah's Witnesses base their "death" doctrine mostly on the book of Ecclesiastes, which indicates that when you're dead, you're dead. The only problem is that we don't know who wrote Ecclesiastes, but whoever it was, it wasn't a prophet. If it was Solomon, he was writing at the end of his life and he had ruined that life by taking pagan wives who used his influence to erect pagan edifaces against the will of the Lord. He was bitter and dejected at that point and his writing was a philosophical one and not an eschatological one. In other words, it was not doctrinal.
When Jesus healed the blind man, the disciples asked, "Master, who did sin, this man or his parents that he was born blind?" Jesus did not correct them or tell them they knew not the scriptures. He said, "Neither hath this man sinned nor his parents...." Thus, there was the implication that the man lived before he was born. Not reincarnation, but a spiritual existence.
The Lord spoke unto Jeremiah: "Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee, and I ordained thee a prophet unto the nations." (Jeremiah 1:5) And in Revelation, John twice falls to the ground to worship the angel speaking to him. Yet what did the angel say? "See thou do it not: for I am thy fellowservant, and of thy brethren the prophets, and of them which keep the sayings of this book: worship God." (Rev. 22:9)
This shows that the angel who spoke to John was once a prophet, like John. He was not dead in the grave, but was alive and acting as an angel. Thus, people live before they were born and after they die. Origen, one of the greatest Christian fathers, wrote: "After death, I think the saints go to Paradise, a place of teaching, a school of the spirits in which everything they saw on earth will be made clear to them. Those who were pure in heart will progress more rapidly, reaching the kingdom of heaven by definite steps or degrees."
Based on scripture and near death experiences, Jehovah's Witnesses most likely will be more likely to learn the truth when they see their own bodies lying in the street or in hospital beds. Then they'll realize that what they've been taught was wrong, and then they'll be more willing to learn. In other words, it would take a very dedicated JW to still believe in the religion once they die and discover they haven't ceased to exist after all. I imagine, too, that most will be relieved.