Matthew 25:46 - "And these shall go away into everlasting punishment: but the righteous into life eternal."
Here are some excerpts from Ron Rhodes' book "Reasoning From the Scriptures with the Jehovah's Witnesses" that I think are pertinent to this thread:
"The punishment spoken of in Matthew 25:46 cannot be defined as a nonsuffering extinction of consciousness. Indeed, if actual suffering is lacking, then so is punishment. Let us be clear in this: punishment entails suffering. And suffering necessarily entails consciousness. Bible scholar John Gerstner comments, 'One can exist and not be punished; but no one can be punished and not exist. Annihilation means the obliteration of existence and anything that pertains to existence, such as punishment. Annihilation avoids punishment, rather than encountering it.' " (pg. 331)
"How do we know that the punishment in Matthew 25:46 does not entail an extinction of consciousness and annihilation? There are many evidences. For example, consider the fact that there are no degrees of annihilation. As Bible scholar Alan Gomes explains it, 'one is either annihilated or one is not. In contrast, the Scripture teaches that there will be degrees of punishment on the day of judgment (Matt. 10:15; 11:21-24; 16:27; Luke 12:47-48; John 15:22; Heb. 10:29; Rev. 20:11-15; 22:12, etc.)' The very fact that people will suffer degrees of punishment in hell shows that annihilation or the extinction of consciousness is not taught in Matthew 25:46 or anywhere else in Scripture. These are incompatible concepts." (pg. 332)
"Moreover, one cannot deny that for a person who is suffering excruciating pain, the extinction of his or her consciousness would actually be a blessing, not a punishment. As theologian William Shedd notes, 'The guilty and remorseful have, in all ages, deemed the extinction of consciousness after death to be a blessing; but the advocate of conditional immortality explains it to be a curse.' Any honest seeker after truth must admit that one cannot define eternal punishment as an extinction of consciousness.
Torment cannot, by definition, be anything but conscious torment. One cannot torment a tree, a rock, or a house. By its very nature, being tormented requires consciousness. Alan Gomes comments, 'A punishment that is not felt is not punishment..."
Note also in Matthew 25:46 that this punishment is said to be eternal. There is no way that annihiliationism or an extinction of consciousness can be forced into this passage. Indeed, the adjective "aionion" in this verse means "everlasting, without end." ...this same adjective is predicated of God (the "eternal" God) in Romans 16:26, 1 Timothy 1:7, Hebrews 9:14, 13:8, and Revelation 4:9. The punishment of the wicked is just as eternal as the forever existence of our eternal God. Moreover, as Professor Gomes notes,
What is particularly determinative here is the fact that the
duration of punishment for the wicked forms a parallel with
the duration of life for the righteous: the adjective "aionios"
is used to describe both the length of punishment for the
wicked and the length of eternal life for the righteous. One
cannot limit the duration of punishment for the wicked with-
out at the same time limiting the duration of eternal life for
the redeemed. It would do violence to the parallel to give it
an unlimited signification in the case of eternal life, but a
limited one when applied to the punishment of the wicked.
Selah.