“Where does it say Christ “slays every ungodly person” at the end of the tribulation?”
Matthew 13 and Luke 19 talk about this “end of the age”—this age prior to the Millennial reign. They aren’t going to just go on living since the King will rule with an iron fist at this point.
“Or that Christ takes away all of His people, never to return to Earth?”
They clearly return with Christ in Revelation 19 & 20 to reign with Him.
“Matthew 13 and Luke 19 talk about this “end of the age”—this age prior to the Millennial reign.”
Where is your evidence that “end of the age” refers specifically to the time before the millennium?
It seems to me that the events described in the passages that you cite are the same as the ones Revelation talks about happening after the millenium, in more specific detail. Why should we rely on passages that speak in parables with a vague reference to time in favor of the detailed passages with a more specific timeline?