"God's plan is 'to sum up all in Christ, the things in heaven and the things on earth' (Eph.1:10), 'to reconcile all things to Himself' whether things on earth or things in heaven' (Col. 1:20). This 'all things' is not limitted to human beings; it includes the whole cosmos, which, according to Romans 8:19ff., is awaiting its liberation from the bondage of corruption...The 'all things' is so comprehensive that it must include even the principalities and powers, the Thrones and Dominations, the angels and archangels, and, in a way that is hidden from us, even the 'demons' and the 'spirits in prison' (1 Peter 3:19)."
("Dare We Hope That All Men Might Be Saved," by Hans Urst Von Balthasar--Roman Catholic Theologian, p. 49.)

"Hell exists as a final possibility, but several of the Fathers have none the less believed that in the end all will be reconciled to God. It is heretical to say that all must be saved, for this is to deny free will; but it is legitimate to hope that all may be saved."
(Kallistos Ware, Greek Orthodox Theologian.)

"...the devil is always our adversary; we should not enter into any kind of negotiations with him, whether by praying for him or in other ways. His salvation is quite simply none of our bussiness...Let us therefore leave the devil and his fate to God, and let us concentrate on our own relationship with God..." 
(Kallistos Ware.)

"The Church has not dogmatically defined the irrevocability of the angels' fall."
(Balthasar, Theo-Drama IV, p. 456.)