The Bible makes it very clear that in the last days you will have one or you will have the other. There isn't a third group.
There are two things that are going to happen when Christ returns....you either meet Christ in the air or you will be slain by the brightness of His coming. There is no mention of a third group.
That being said, to receive the mark of the beast you must willingly ACCEPT the mark and worship the image of the beast. If you have God in your thoughts, you will not do this. However, it's not a default situation...if you're sealed you don't have to worry about the mark at all, but of course it takes some decisions on your part before the return of Christ. That's why it's important to know what the seal of God is along with how you get it.
Revelation 14:9-10 gives this warning: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,
10 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:
REPENT
NOW...AVOID THE RUSH ON JUDGMENT DAY. (I love that quote)
It all comes down to "who do you serve?" Do you serve God or Satan? The great controversy.
.....but as for me and my house, we will serve the LORD.