What is meant by the Jehovah's Witness statement “Jesus was dead, forever dead.”? Here are a number of quotations from their literature on the subject:
Studies in the Scriptures Volume 5 (1899 p 454) The At-one-ment Between God and Man: “… for the man Jesus is dead, forever dead…”
We deny that he was raised in the flesh, and challenge any statement to that effect as being unscriptural.” (Studies in the Scriptures, Vol. 7, p 47)
The Kingdom Is At Hand (1944 p 258): “At death he laid aside the human organism in which he ministered as a new creature for three and a half years; and in his resurrection he was no more human.”
Jesus’ fleshly body “was disposed of by Jehovah God, dissolved into its constitutive elements or atoms.” (The Watchtower, Bound Volume 1953, p 518)
Things in which it is impossible for God to Lie (1965 p 354): “The human body of flesh, which Jesus Christ laid down forever as a ransom sacrifice, was disposed of by God’s power…”
"Michael was willing to leave heaven and to be born on earth as a human. Jehovah sent his only begotten Son to earth by transferring his life force from heaven into the womb of a virgin named Mary. In transferring his life force into Mary's womb, the heavenly Word of God divested himself of everything as a God-like spirit except his impersonal life force, including his body and personality." (Awake! 8 August 1972, p27; Aid to Bible Understanding, 1971, p 1061)
You Can Live Forever in Paradise on Earth, 1982 pp 143-144) "Jesus did not rise from the dead in the same body he died in."
Reasoning from the Scriptures (1985 p 218): “So the evidence indicates that the Son of God was known as Michael before he came to earth and is known also by that name since his return to heaven where he resides as the glorified spirit Son of God.”
What Does The Bible Really Teach? Appendix, Who is Michael the Archangel? (2006, pp 218-219):
“The Bible indicates that Michael is another name for Jesus Christ, before and after his life on earth… This scripture therefore suggests that Jesus himself is the archangel Michael… so the Bible speaks of both Michael and ‘his angels’ and Jesus and ‘his angels.’ Since God’s Word nowhere indicates that there are two armies of faithful angels in heaven… it is logical to conclude that Michael is none other than Jesus Christ in his heavenly role.”
This is a partial quote from an article showing how Jehovah's Witnesses do not expect that Jesus will ever return visibly:
Awake! 22 July 1973 pp 3-6: Christ’s Return—Will You See It?
By and large, those who expect Jesus personally to come again expect to see him literally, in his human form. Many even believe that they will see him in the very same body he had when on earth and in which he was put to death. In support of their belief that they will see him with their physical eyes, they quote such scriptures as Revelation 1:7, which reads: “Look! He is coming with the clouds, and every eye will see him.” What does this actually mean?
That Jesus will not return in a physical body is clear from the testimony of the Scriptures (Matthew 20:28 and John 6:51)... As to Jesus’ condition since his resurrection and ascension to heaven, God’s Word says: “He is the reflection of [God’s] glory and the exact representation of his very being.” (Heb. 1:3) So he must be a spirit being, just as “God is a Spirit.”—John 4:24.
This being the case, will Jesus ever again take on a corruptible body of flesh in order to be seen by humans who are too frail to endure the sight of his glorified spirit body? That is not God’s purpose respecting his Son. As the inspired apostle Paul said on one occasion: “[God] resurrected him from the dead destined no more to return to corruption.”—Acts 13:34.
Accordingly, when the Scriptures speak of “every eye” as seeing Jesus, this is manifestly to be understood in a figurative sense. As a result of what humans see and hear on earth, they will perceive that the events taking place are because Jesus Christ is taking a personal hand in the affairs of mankind.—Rev. 11:15; 12:10-12.
It is noteworthy that Christians believe Jesus will return, accompanied by all the heavenly hosts (including Michael the Archangel) in a glorified body - the one he was resurrected in.
Jehovah’s Witnesses believe that the Word of God was Michael the Archangel before he left heaven to become Jesus. The life of the spirit creature Michael was transferred to Mary’s womb and he was born fully human. Jesus the man, died, and what came out of the tomb was a spirit creature, known in heaven as Michael the Archangel.
What does this mean, that Jesus the man is dead, forever dead? According to Jehovah's Witnesses it means Jesus will never come back as a man. He was resurrected to heaven as a spirit creature, his body conveniently disappearing. Furthermore, they claim that Jesus took up his heavenly throne invisibly in 1914 – that was the second coming – and Jesus is not coming back to earth.
From what I've read it seems that Jehovah's Witnesses believe that the life-force of Michael the Archangel was transferred into the body that became Jesus, the man, but Jesus, the man, did not come out of the tomb, his body simply "disappeared". They insist that Jesus was resurrected, only it was a spirit body. They deny the phyiscal resurrection of Jesus.
At Armageddon it will be the mighty Michael the Archangel who defeats Satan and all who follow him. Jesus, the man, is dead - forever dead.
Additional official J.W. information regarding Jesus' resurrected body:
Another regarding Jesus' invisible return with the angels: https://www.jw.org/en/bible-teachings/questions/jesus-coming/