Once the person receives the mark of the beast, there will be no more hope of salvation for him or her. The reason is, that the Bible clearly states that worship of the beast is involved with the acceptance of the 666.
The verses in the video: Revelation 14:9-11(a)
9 A third angel followed them and said in a loud voice: “If anyone worships the beast and its image and receives its mark on their forehead or on their hand, 10 they, too, will drink the wine of God’s fury, which has been poured full strength into the cup of his wrath. They will be tormented with burning sulfur in the presence of the holy angels and of the Lamb. 11…for ever and ever. There will be no rest day or night