Indeed st. Gregory of Nyssa talked about future restoration ("apokatastasis" in greek) of every human in the Reign of God. He was talking about restoration of nature, not restoration of consent. So, he was not talking about the Origenian restoration of will. Acts 3:21 “whom heaven must receive until the period of restoration of all things about which God spoke by the mouth of His holy prophets from ancient time“.
In this context the "hell" is not a natural torment, but a personal torment experienced from human beings that will have a restored perfect nature. Hell is declared as everlasting in each and every Orthodox Ecumenical Council. Matthew 25:46 "These will go away into eternal punishment, but the righteous into eternal life." - Jude 1:6 “And angels who did not keep their own domain, but abandoned their proper abode, He has kept in eternal bonds under darkness for the judgment of the great day,..”
St. Gregory is indeed the "father of fathers" !!
If the "second coming" was an earthly coming then there would have been expected a third coming as the final one, because Christ said John 18:36 "..."My kingdom is not of this world. If My kingdom were of this world, then My servants would be fighting so that I would not be handed over to the Jews; but as it is, My kingdom is not of this realm."
We expect a final second coming "not of this world" because: (2 Peter 3:13) “But in keeping with His promise we are looking forward to a new heaven and a new earth, the home of righteousness.” - (Revelation 21:1)”Then I saw a new heaven and a new earth; for the first heaven and the first earth passed away, and there is no longer any sea.”