Perhaps the following passage explains how he could maintain both positions:
“For the destruction of the last enemy must be understood in this way, not that its substance which was made by God shall perish, but that the hostile purpose and will which proceeded, not from God but from itself, will come to an end. It will be destroyed, therefore, not in the sense of ceasing to exist, but of being no longer an enemy and no longer death. For to the Almighty nothing is impossible, nor is anything beyond the reach of cure by its maker.”In this case, it might be that Origen denied that Satan would be saved for "Satan" is to Lucifer what "the sinful nature"/"the flesh"/"the old man" is to us. For God to save us "the old must pass away" and there must be new creation (2 Cor 5). So perhaps, for God to redeem fallen angels he must annihilate their demonic aspect. Thus it would be that Satan and his demons would be lost forever — damned — even as God saves Lucifer and his angelic followers.
Peri Archon 3.6.5
(trans. Marguerite Harl, Gilles Dorival, and Alain Le Boulluec. Paris, 1976, p.67)
Gregory of Nyssa was even more bold than Origen on this issue: He maintained that "the originator of evil himself will be healed” (Catechetical Orations 26. The Catechetical Oration of Gregory of Nyssa. Edited by James H. Srawley. Cambridge, 1903, p. 101).
Again, it partly depends on what you think of the ontology of "the demonic." If you do not think that Satan and evil spirits are individual persons, created good yet now fallen (and there are various ways in which one may try to make that move), then they are essentially evil forces and thus irredeemable. But if you do take the classical view that demons are rational souls — non-human persons — then there is something to be said for the approach of Origen and Gregory. Food for thought.