To make it about a 1000 year reign of Christ on earth misses the context.
A reign on earth is the only context after a period of tribulation.
Are we to assume that John is referring to Christians prior to the birth of Christ, who were beheaded during a never mentined Great Tribulation, and people who never even heard of Christ who was not born yet, will now reign for thousands of years with Jesus after His birth, death, resurrection, and ascension into heaven?
Revelation 20 mentions nothing about reigning on earth during tribulation, nor reigning in heaven while others are on earth in great tribulation. These people mentioned in Revelation 20:4 did not remain faithful, but had their head chopped off to avoid the mark. No one could endure until the end. They either received the mark or chopped off their head. Only those without a head received life again. No one who endured were even mentioned. So you are adding words and thoughts into the chapter that are not even mentioned. How is not having a head enduring until the end in any imagined scenario, even possible? I thought enduring until the end meant while a person still had a head?
You have added to the text of Revelation 20 that some remained faithful even to the death, while assuming others remained faithful until the end. This is all an assumption, as no one could remain to the end, unless they had received the mark. This mark was not something physical given by humans. This mark was spiritual meaning that person had been removed from the Lamb's book of life by God, so a physical mark that others could see, given by God, as a spiritual mark showing one could no longer be redeemed. In order to be redeemed one had to chop off their head. That was the only decision made in faith, with no one ever experiencing a resurrection from such a decision. We know the end result, they may have been able to read Revelation 20, who knows. But it was still an act of faith, not something that happened to a Christian. They were not martyred. The only means of escape was to chop one's head off. If one chose to keep their head, then God would place the mark on that person.
At that point, only two types of humans were left on the earth. Those with a mark, and those without a head. It would be impossible to endure until the end of this period of time without a head, as that means they were dead, and not enduring.
This verse describes that point exactly:
"I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years."
This verse never mentions any one still alive, but only those who were beheaded. Nor does it say they died while reigning with Christ. The reigning was after they were beheaded, and also after being made alive. They had to actually live first after being beheaded, to be able to reign. They did not reign while still beheaded, nor prior to being beheaded.
You cannot just change the order of these words around and form some kind of theory that says, "It would make more sense if we changed these words around to make a different point than the one John actually wrote".