It is interesting that many authors in the early church motivate the incarnation by appeal to the impropriety that God's creation should have been undone and destroyed. This implies a great many things about the Christian conception of creation, of divine-human relations, of God's values and character, etc.
Take for instance this passage:
But since it was to come to pass that some also should fall away from life, and bring death upon themselves by their declension -- for death is nothing more than a departure from life -- and as it was not to follow that those beings which had once been created by God for the enjoyment of life should utterly perish, it was necessary that, before death, there should be in existence such a power as would destroy the coming death, and that there should be a resurrection, the type of which was in our Lord and Savior, and that this resurrection should have its ground in the word and life of God (Origen, De principiis II.4).
Here Origen says that those creatures which had fallen were created by God for the enjoyment of life. I've repeated this point in past posts, but it is worth repeating again and again: the Bible teaches that God created the world for its own sake, so that it may flourish and enjoy fellowship with him. The Augustinian notion that God creates some creatures for his own ends, whether to show his mercy or else to damn them for their sins and show his justice, is foreign to the biblical story. It is closer to the Babylonian Atrahasis myth, where the gods create humanity to do hard labor for them when they get tired of it. Genesis, on the other hand, portrays God as fundamentally interested in the world for its own sake. This picture Origen passes along as well, when he says that God created those who'd fallen and all things for the enjoyment of life.
Interestingly, too, for Origen there was also the problem of God's sovereignty and its compromise by the fall. He doesn't use this language explicitly, but it is arguably implicit in what he writes. He says that it was not to follow that what God created for one fate should suffer another. Why shouldn't it follow? Why the strong language? Because it is a compromise of the sovereignty and rule of God. That is why, when what he intends does not come about, he does not merely adjust to the new reality or accept it weakly, but takes control of things and works towards its realization. God's sovereignty must be affirmed even in the face of the free disagreement and apostasy of his creatures, but of course not by violence to their wills.
A similar sentiment is affirmed by Athanasius:
It was unworthy of the goodness of God that creatures made by Him should be brought to nothing through the deceit wrought upon man by the devil; and it was supremely unfitting that the work of God in mankind should disappear, either through their own negligence or through the deceit of evil spirits. . . . Surely it would have been better never to have been created at all than, having been created, to be neglected and perish; and, besides that, such indifference to the ruin of His own work before His very eyes would argue not goodness in God but limitation, and that far more than if He had never created men at all. It was impossible, therefore, that God should leave man to be carried off by corruption, because it would be unfitting and unworthy of Himself (Athanasius, De Incarnatione 6).
Here Athanasius stresses God's quality as a good creator. Precisely because he is a good creator he does not allow that what he has created come undone and be destroyed. To do so would have been beneath God, unfitting and unworthy of Himself. Interestingly Athanasius stresses that this is true even if the downfall of a creature should be deserved, its own fault. Even in such a case as this, to fail to act to save and restore the creature would betray indifference.
Athanasius speaks contrary to the likes of Oliver Crisp, who argues in "Is universalism a problem for particularists?" Scottish Journal of Theology 63, no. 01 (2010): 1-23, that it would be no mark against the goodness of God not to save anyone at all, since salvation is a matter of grace. The confusion here is between justice and goodness: that salvation is a matter of grace speaks against the demand for salvation by justice, by merit or desert; but goodness is the disposition to do good to others, irrespective of merit, and Athanasius sees that it would be contrary to God's goodness to allow his creation to be destroyed. Here, too, we find a sentiment utterly opposite of the Augustinian spirit of Crisp's article: God's goodness as creator is at stake, and therefore his salvific intentions and acts are aimed at the whole of creation.
Gregory of Nazianzus shares this sentiment too, affirming that it would not be consistent with God's nature to allow mankind to be separated from God:
But to despise man, when by the envy of the Devil and the bitter taste of sin he was pitiably severed from God his Maker — this was not in the Nature of God. What then was done, and what is the great Mystery that concerns us? An innovation is made upon nature, and God is made Man. “He that rideth upon the Heaven of Heavens in the East” of His own glory and Majesty, is glorified in the West of our meanness and lowliness (Oratio 39.13).
It is important to note, of course, that this principle, if taken seriously, issues a universalist conclusion. If the destruction of the creation is beneath God and unworthy of him, to use Athanasius' language, and contrary to God's intentions and (consequently) his sovereignty, to use Origen's, and incompatible with his nature, to use Gregory's, then what else must God do except save the creation? Anything less than this would be a failure and a black mark on God's white robe: a failure to save would speak either weakness or else malevolence or indifference.
Someone may respond that, because of man's freedom, God cannot guarantee this result. But in response I will argue in the language of these titanic teachers of theology, and condemn such a response as blasphemous and irreligious on the grounds that it ascribes weakness to God. Certainly man is free and acts independently of God, but we don't infer from this that therefore the Lord is too weak to get what he wants in his own world, or that he has no means of accomplishing what he wills with the cooperation of the will of man.
Suppose you press the point and ask: How, then, will they be saved? I don't have to tell you; and unless you are a heretic, there a million theological questions you can't answer, either, such as the nature of the Trinity, how the two natures are united in Christ, and so on. What is one more mystery?