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God will send strong delusions to confuse those that are left. The Holy Spirit will also leave the planet.
However, Christians will be persecuted.
That can only mean that many of the Christians that are left behind, those that never were truly saved, will understand exactly what has happened.
They will be trying to spread the word, and I feel many of them will then be saved.
They will also not take the mark of the beast, which means just surviving will be EXTREMELY difficult.
Sadly, it will be almost impossible for the non Christians to be saved.