While Jehovah's Witnesses definitely do not believe the same thing that the Sadducees believed, what we believe has some things in common with what you described.
We do believe in spirit creatures, including God and angels, and we believe in heaven. (John 4:24) But we don't believe that humans have a spirit person inside them that survives the death of the physical body and continues to exist in spirit form. When a person dies, they are just a dead body, and their consciousness ceases to exist. (Ecclesiastes 9:5, 6) In that sense you could say we don't believe in an afterlife, but we do believe God can and will resurrect many humans back to physical earthly life in the future. (Acts 24:15) Basically, he will recreate them from his memory. (Job 14:14, 15)
We believe that the spiritual heavens and the physical world, are different things. When God created humans, he had already created spirit angels, so humans were meant to be different, physical beings. (Job 38:4, 7) The physical earth was intended to be our home, not heaven. (Psalm 115: 16) So most of the blessings and curses discussed in the Bible, as they relate to humans, are about things we would experience on the earth, at least in the Hebrew and Aramaic scriptures. Those that continue to obey God can live forever on the earth. (Psalm 37:29) Those that are judged negatively will die and remain dead forever. (Psalm 37:9, 10) The gift of life will have been taken away from them. Just as they did not exist before their life began, they will not exist after it ends. (Genesis 2:7, 3:19)
Of course the Christian Greek Scriptures do speak of a heavenly resurrection. (1 Corinthians 15:42-44) But that was not a hope that was always held out to people. It is something God later opened up in order to serve a limited purpose. 144,000 people are being selected from among mankind, to rule with Christ in heaven as kings and priests. (Luke 12:32, Revelation 14:1, Revelation 1:6) Because they experienced life as imperfect humans, they will be able to empathize with and relate to the rest of mankind. Depending on how you define it, one might still say that those resurrected to spirit life are not exactly experiencing an "afterlife". It is not as if they have a spirit that survives the death of the body and they continue to exist in that form. They first completely die, and then God recreates, or resurrects them in a different form, a spirit one. (1 Corinthians 15:50)