I’ve been part of a very long argument in Controversial Theology about this. It’s gotten too ugly to be useful. But as a result I’ve looked at a number of the key passages. For me as a liberal Christian, Jesus’ own teachings are the standard. But even Jesus seems to spoken in different ways:
* In several passages he talks about judgement in terms of fire. Several of the more explicit passages seem to imply a fire that destroys.
* the term Gehenna is used (translated hell in NRSV); it is sometimes associated with fire
* another image is the outer darkness, with weeping and gnashing of teeth
* the rich man in Luke 16:19 is being tormented in Hades (note that Hades is not the same thing as Gehenna, and may well be temporary)
* “eternal punishment” is used once, Mat 25:46, and “eternal fire” twice, Mat 18:8 25:41
It is challenging to produce a single description from all of these. Liberal exegesis tends to take typical usage over unusual or extreme usage. (This is the opposite of conservative exegesis, which tends to take the most extreme usage as controlling.) So I’m going to assume that the overall picture is of exclusion and destruction. I think the references to eternal fire can easily be understood using OT example, in which the fire is eternal, but things thrown into it aren’t. I think Luke 16:19 might well have used current Jewish imagery to make a point.
But if we take Jesus’ typical descriptions, I think we have to assume that he intended both being thrown into outer darkness and being burned up by chaff as the same thing. I’d say Jesus didn’t intend to teach a specific literal future for those who are excluded. Could exclusion and destruction reasonably both be reasonable images for the same thing? Sure. I doubt that someone permanently excluded from contact with the source of life is going to have much existence left. Whether they are directly destroyed, as suggested by the fire image, or just fade into nothing, as suggested by the outer darkness, doesn’t seem much of a difference.
Here's N T Wright's speculation, which I think is consistent with both, though perhaps more so with outer darkness.
“I don’t find any of these three traditional options completely satisfactory, but I think a somewhat different form of conditionalism may be the best we can do. We should of course always stress that the question of who shall eventually be saved is up to God and God alone, and that we can never say of anyone for certain, including Hitler and bin Laden, that they have gone so far down the road of wickedness that they are beyond redemption. I take it, however, that there are many who do continue down that road to the bitter end. How can we think wisely and biblically about their fate?”
“The central fact about humans in the Bible is that they bear the image of God (Genesis 1.26-8, etc.). … But they can only be maintained in his image, as genuine humans, by worshipping him; they depend on him for their life and character. The rest of creation, by contrast, is subject to decay and death. If we worship it, or some part of it, instead of the life-giving God, we are invoking death upon ourselves instead of life.
“This opens up a possibility: that a human being who continually and with settled intent worships that which is not God can ultimately cease completely to bear God’s image. Such a creature would become, in other words, ex-human: a creature that once bore the image of God but does so no longer, and can never do so again. Humans do, I believe, possess the freedom (some would say even the ‘right’, but I think that is difficult language at this point) to choose to worship creation rather than the creator. The God who made them and loves them grants them that freedom, even though they may misuse it. The New Testament indicates strongly that there are some, perhaps many, who go that route.”
Wright considers this a type of conditionalism. However I first ran into this by a book by a Catholic author, advocating a traditional view of hell. So the idea of eternal punishment and annihilation may in fact have some room for overlap. I would call what Wright describes destruction or second death.