They are
given eternal life. They aren't originally immortal. Consider this:
Genesis 3:22-24
And the Lord God said, “The man has now become like one of us, knowing good and evil. He must not be allowed to reach out his hand and take also from the tree of life and eat, and live forever.” So the Lord God banished him from the Garden of Eden to work the ground from which he had been taken. After he drove the man out, he placed on the east side of the Garden of Eden cherubim and a flaming sword flashing back and forth to guard the way to the tree of life.
Revelation 2:7, 22:2, 22:14, 22:19 also talk about the tree of life and that is associated with eternal life.
So in Genesis you're saying that they were already immortal... but that doesn't seem to be the case in the passage I quoted. I guess this will be yet another time that you completely ignore one of my major points.
How are the damned to suffer eternal torment, as described, if nothing remains to experience eternal damnation?
They'd burn in an "unquenchable fire" (see post #138) and be destroyed. See post #126: "Their sentence and punishment of death will last forever", etc. (if you read all of that one page website you'd see other points as well)
Without soul, an immortal entity,
Souls don't have to be immortal.
e.g.
https://www.jewishnotgreek.com/#B"Among major schools of Greek thought, only Epicureans denied the soul's immortality." (Craig S. Keener, The IVP Bible Background Commentary New Testament, Downers Grove, Inter Varsity Press, 1993, p.374)
"...'immortality of the soul,' as normally understood, is not a Biblical doctrine" (The International Bible Commentary, second edition, Grand Rapids, MI, Zondervan Publishing House, 1986, p.60 column 2)
how are the saved to experience their reward?
They could be given eternal life.
You can't have one without the other. The dead experience nothing.
I think according to some parts of the Bible the dead sit in the ground then one day they are resurrected... then if they are sent to hell they could burn up or be given eternal life....