the concept of cesing to exist dose not exist in the thoughts of the aichant world, the Church Fathers included. Even the concept of returning to nothingness comes form the modern Philosophical thought. All people in the ainchant world believed in some form of continuing life, from Sihol and Hadys, to the Indian beliefs in reincarnation, but never has their been a belief that humans cease to exist at the death of the body.
The reason it is not written on is that until the last Century it did not exist as a thourght and most Orthodox theologans have never come up against it, so have never written on it. Their concern has been to reject other beliefs in life after death not to challenge a belief in a lack of life after death as this has never been held by people before very recent times.
From what I understand of the fathers and the recent saints (St Siluan in particular) is that the human soul is immortal and will not cease to exist. Many of the writings of the desert fathers speak of the reality of suffering those who died without the knowledge of Christ. St Siluan also speaks of praying for all, especially those who do not know Christ and those suffering in torment. From what I understand the saints believed in the possibility of being of condemed for eternity and the desired that none suffer this fate.
Annihilation is a recent development form Protistant theology, and sporns from an unwillingness to accept that people will suffer for eternity, despite this being clearly written in the Gospels and the doctrines of the fathers. we speak of the resection of the dead and everlasting life in the Creed, this is not a resurrection of the saints alone but all, then the judgment. It in part comes from reading of the fathers without the gidence of holy tradition and an unwillingness to accept that God will see through on his promesses,as he as always done so. No one before the skisam held the view and only some of the more wayward thinkers of the reformation thought of it. From what I understand of tradition it would be classed with the hysterics and condemned by the church, but as not orthodox christian has been lead astray no bishop has seen fit to deal with it. As a understanding the church in her people have not accepted it and so although their is no formal condemnation their has not needed to be one as it has not become an issue to the church, due to the inplicet condemnation of it as contery tot he creed.