>> What? Just a warning? No, it's definite.
In the meeting in the year 430 after Rome receives the documents supposedly written by Augustine on his deathbed, the Last Challenge is described as being about corruption in the Church. Specifically, Satan is said to have claimed in the late first century that, by the End Times, the Church will be so corrupt that Christ will not find even one priest worthy of Heaven. That ruse is used by Satan because it supports the narrative that the Emissary is holy and has come to purge the Church of corruption. In reality, it allows Connor to purge the Church of his enemies (real priests still dedicated to God).
So, when Satan, who is in the meeting as a corporeal, discusses the Last Challenge, he explains to the others that, since God accepted the Last Challenge, there is no way the existing ending of Revelation can describe what will actually happen since it does not account for the events related to the challenge. In fact, it was the existing ending of Revelation that led Satan to issue the challenge. He adds that, had it been mentioned in Revelation, along with the likely outcome (God wins), Satan would never have issued the challenge. So, regardless of what John of Patmos wrote, Satan would have done something different to try to "change" the ending.
So, were John's ending "real", Satan would have invalidated it simply by issuing the Last Challenge (assuming God accepted). Although there is precedent in the Bible to change a "prophecy" (the people of Nineveh escaped destruction in the Book of Jonah), for now, I'm going to have Satan go with the argument that Revelation's ending is just a warning, so i don't need to justify how my ending could possibly change one of the biggest prophecies in the Bible. Technically, one could argue that Jonah's prophecy was also just a warning, so no prophecy was actually altered.