That's true, sbf, humans on earth who aren't given immortality, per the WTS, definitely can be destroyed and jws readily believe that. But many jws believe immortality means Jesus and the 144,000 in heaven cannot die or be killed. Of course, the discussion of this was back in the 50's.
*** w56 4/1 p. 219 Questions From Readers ***
An answer in the November 15, 1955, Watchtower said Jehovah could, if he wished, destroy even an immortal creature. The booklet What Do the Scriptures Say About “Survival After Death”? says that if the demons had originally been created immortal they could not be destroyed from the universe. Which is correct?—J. L., United States.The statement in the booklet about survival after death refers to immortality according to its basic meaning of deathlessness, indestructibleness. The other statement about God’s ability to destroy even an immortal creature rested upon the view that he is absolutely almighty without any limitation upon his own power by even himself. So this latter statement presented what seems in accord with this view. However, it enters into the realm of speculation, because it is in fact based on a speculative question.
*** w55 11/15 pp. 702-703 Questions From Readers ***
Can man sin after the final test at the end of the thousand-year reign, and if he did could Jehovah put him to death, since Revelation 20:14 and 21:4 (NW) say “death and Hades were hurled into the lake of fire” and “death will be no more”?—J. M., Mexico.
The death spoken of here is the death due to Adam’s sin, and then it will not have any power over mankind. Even its past effects will be nullified by the resurrection of its victims. All who are to remain permanently dead or in second death will be in that condition because of willful indifference or wickedness. So in the new world there will be no death due to Adamic sin.
But the passing of the final test at the end of the thousand years will not make men into robots. They will still be free moral agents, choosing their own course of conduct. Hence they could sin if they chose to do so. And if they did, Jehovah, with whom nothing is impossible, could put them to death, and it would be no contradiction of the above scriptures, since this death would not be Adamic death. We cannot conceive of the Creator’s being powerless to destroy a rebellious creature. He is the Almighty God. And the lake of fire, a symbol of second death, exists forever, which would suggest that any creatures becoming rebellious could be pitched into it by being destroyed.
On the other hand, we need not expect any such happenings. Jehovah made man, knows him inside out and knows how to test him to see how he will use his freedom of choice. So we may have complete confidence in the thoroughness of the test at the end of the thousand years, that it will ferret out all the unworthy ones and eliminate them, leaving only those of demonstrated reliability, in whom confidence can be placed, just as Jehovah accurately judged Job and knew he would not deflect even under extreme satanic pressure. For any to sin after passing the final test would imply that the test was faulty, that Jehovah was unable to test with sufficient searchingness. But his test will be a success and accomplish its purpose of weeding out any who would ever misuse their freedom of choice to choose sin.
Reasoning in the same way, there will be no danger of any of the heavenly class who have gained immortality later choosing to sin, and thus awkwardly having in the universe immortal rebels. But here again, even if such a thing did happen, we need not think that Jehovah would be powerless. Jehovah could destroy even an immortal creature. Immortality means to have the power of life within oneself. In other words, such a creature is not dependent on any outside source or environment to replenish energy or for the continuance of the life processes. Human creatures must eat, and spirit creatures apparently draw upon an outside source for continued existence, but immortal ones would not have to do this. They cannot die from a lack in their environment, but have life complete in themselves. Nevertheless, the all-powerful Jehovah could terminate their existence if he decided to do so.
Hence we are letting the statement in the booklet stand, in accord with the meaning of absolute immortality as conveyed in the Holy Scriptures. A fuller discussion on this may be expected in time in the columns of The Watchtower.