If eternal punishment is false simply because God didn’t directly tell Adam, then the same logic applies to the resurrection of the dead. Example using their own words……
How might we reason with an individual who claims that there is a resurrection from the dead? First, we could assure him that the wicked will be punished (2 Thess. 1:9). Then, we could have him read Genesis 2:16, 17, which shows that the penalty for sin is death. We might explain that by his sin, Adam caused the entire human race to be born as sinners (Rom. 5:12). But we can point out that God said nothing to Adam about being brought new life through Jesus Christ (Rom. 5:21). We could then ask, “If Adam and Eve were in danger of being returned to dust forever, would it not have been fair to tell them the truth about the resurrection of the dead?” (Luke 20:35). We could then read Genesis 3:19, where sentence was pronounced after their sin but nothing was said about resurrection. Instead, Adam was told that he would return to the dust. Would it not have been fair to let Adam know that a savior would come, and even though he returned to dust that it would be possible for him to be redeemed and resurrected to immortal glory? Would it have been fair to tell Adam that he would go back to the ground if he was really going to be resurrected again?
That’s a horribly bad argument that is actually challenging God’s sovereignty.
Along with physical bodily death as punishment for sin, the book of Revelation speaks of another “death” and even identifies it as “the second death, the lake of fire. Furthermore, whoever was not found written in the book of life was hurled into the lake of fire” (Rev 20:14-15). The beast and the false prophet, “while still alive, they both were hurled into the fiery lake”, but others were physically killed before being thrown into the lake of fire (Rev 19:20-21). The devil and his followers from among the nations are also thrown into the lake of fire “where the beast and the false prophet already were, and they will be tormented day and night forever and ever”(Rev 20:8-10).
We also know that this is where all the condemned go ”who have been cursed, into the everlasting fire prepared for the Devil and his angels” (Matt. 25:41). And we are also told that they "shall be tormented with fire and sulphur in the sight of the holy angels and in the sight of the Lamb. And the smoke of their torment ascends forever and ever, and day and night they have no rest…” (Rev. 14:10-11). (Note: All scripture quotes are from the Watchtower Bible and Tract Society New World Translation)
How can they be “tormented day and night forever and ever and… have no rest”, if they no longer exist?
Most of the problem with the JW’s in this regard is they really don’t understand “soul” and “spirit”. For example from their Watchtower publication “What Does the Bible Really Teach?”: According to John 4:24, ”God is a spirit…”. It does not say that God has a spirit, but that he IS a spirit. By their own definition, they would have to say that Jehovah God has no feeling and cannot think because he is just an impersonal force like electricity. They do believe that the Holy Spirit is just a “force” (easily shown to be false), but this would have to be applied to Jehovah God according to their definition and according to John 4:24. They are seriously being misguided.
They have a very materialistic view of man because they don’t know what “spirit” is. Since man is purely physical from their perspective, if he is thrown into a lake of fire he will burn up and cannot survive this. Thus he is annihilated. Eternal punishment will not make sense unless they learn to understand the nature of “spirit” IMO…