For based upon his interpretation of various New Testament texts, Augustine insisted that hell is a literal lake of fire in which the damned will experience the horror of everlasting torment; they will experience, that is, the unbearable physical pain of literally being burned forever. The primary purpose of such unending torment, according to Augustine, is not correction, or deterrence, or even the protection of the innocent; nor did he make any claim for it except that it is fully deserved and therefore just. As for how such torment could be even physically possible, Augustine insisted further that “by a miracle of their most omnipotent Creator, they [living creatures who are damned] can burn without being consumed, and suffer without dying” (City of God, Bk. 21, Ch. 9). Such is the metaphysics of hell, as Augustine understood it.
This is an extraordinary misreading of the quoted passage from Augustine. In the sentence quoted, 'they' clearly does not refer to "living creatures who are damned" but to things like salamanders, i.e., beings that were thought to be able to live for a short time in fire. The reason they are relevant in context is that God's ability to create such wonders is thus a reason not to rule out, out of hand, the possibility that Christ's comments in Mark 9 refer to the body, and not just the soul. Nor are we talking about "being burned"; the phrase in ustione sine consumptione means "burning without being burned". Nor does Augustine 'insist' in this chapter on what Talbott claims, because Augustine doesn't think it's possible to know completely what will happen (he goes on at great length in this book arguing that there are things we can't reason certainly about but only know by experience). He is discussing a particular passage of Scripture, Christ's comments about the worm and the fire in Mark 9. He presents three possibilities, that the words of Mark 9 refer only to the spirit, that they refer to both body and soul, and that they refer to body alone; he thinks the first is not a reasonable reading, and he thinks the third is an easier reading of the passage than the second. Of those two, however, he says that everyone should pick the reading they please, recognizing that we do not yet have full knowledge of the things to come. Thus the passage is not metaphysical, but almost entirely exegetical, and the only thing that Augustine insists on here is that bodies will experience pain (if that is how we wish to translate dolor here) from the fire. The animals in the fire example is put forward simply to say that the bodily interpretation of Christ's words cannot be ruled out on grounds that it would make Christ say something impossible. He is not claiming that the damned are like salamanders; he is merely claiming that we can't go around ruling out positions on the ground that God can't make bodies that endure in fire.
This is a common error in reading Augustine, namely, taking some particular thing he says as a categorical assertion. But Augustine's natural style is discursive; he explores rather than lectures. He will rule things out, but he often leaves things open; he will often prefer positions without insisting on them; and he will develop views at length without actually asserting them. He is also much more, as we would say, skeptical than generally recognized; that is, he will often criticize positions for requiring knowledge we could not have. And this is very true whenever he discusses the afterlife; indeed, throughout Book 21 of The City of God he criticizes various positions on this ground. He does think we can and should believe certain things about the afterlife; but this is based on what he thinks is the reasonable range of exegetical positions that can be taken about the explicit statements of Scripture, not on 'metaphysics'. There is no 'metaphysics of hell' in Augustine.