Athanasius clearly affirms a legal atonement. He mentions that after the fall, men are under the “law of death.” It is indeed ontological, life vs. death, but it is also legal, as Adam is being punished for his sin. This is only one half of the dilemma, however. Athanasius believes that God’s glory would be impugned if He failed to keep His word in punishing sin, but he also believes that God’s glory would be impugned if He failed to set creation back to right. God’s nature requires both justice and glorified creation. He explains:
For it were monstrous, firstly, that God, having spoken, should prove false—that, when once He had ordained that man, if he transgressed the commandment, should die the death, after the transgression man should not die, but God’s word should be broken. For God would not be true, if, when He had said we should die, man died not. Again, it were unseemly that creatures once made rational, and having partaken of the Word, should go to ruin, and turn again toward non-existence by the way of corruption. For it were not worthy of God’s goodness that the things He had made should waste away, because of the deceit practised on men by the devil.
~ On the Incarnation 6.3-5