Revelation 20:4 is identifying those who were BEHEADED and martyred for witnessing and testifying of Christ Jesus who did not worship this beast and DID NOT accept the mark that the Beast requires all, both small and great to accept in the way they think and act (forehead and right hand).
It says nothing about a permanent mark there or in any verse in Revelation about this mark. This mark causes all who receive it to be deceived by the Beast - it says nor implies that the small and great receiving this mark are 'permanently marked'. Scripture tells us that the Beast and the False Prophet are thrown into the Lake of fire. It does not say all those with the mark and thrown in with them.
This mark is not permanent. Blasphemy of the Holy Spirit is the only sin that can never be forgiven. The reason for this is because when one hardens their mind and heart to God - it is impossible for that person to accept grace and redemption, and rejects God completely for his own belief system.
Of their own free will they reject Him, and they will wail and gnash their teeth against the Most High rather than repent and accept Jesus as their Lord and Master.
9 And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand, The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb: 11 And the smoke of their torment ascendeth up for ever and ever: and they have no rest day nor night, who worship the beast and his image, and whosoever receiveth the mark of his name.
Revelation 20 is clear that those that received the mark will not be a part of the First Resurrection.
“Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power...”
Where do you see those that received the mark?
“But the rest of the dead lived not again until the thousand years were finished...”
Resurrected unto the GWT judgement!
Not beneficiaries of grace, but on trial.
“And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works.”
What will be the end of those judged “according to their works?”