Hello CV5, you knew that I would show up regarding this claim.
The word here is 'apostasia' translated as 'rebellion, apostasy, falling away, defection, revolt, departure (implying
desertion), etc.
The word 'apostasia' is derived from two words 'apo - away from' and 'histemi - stand,' properly 'away from ones stand, a leaving from a previous standing. This word is used in only one other time in scripture which is found in Acts 21:21
"Now they have been informed about you, that you teach all Jews among the Gentiles
apostasy from Moses, telling them not to circumcise the children nor to walk in the customs."
Therefore, based on the other synonyms of apostasy, the word 'departure' cannot be used to mean to depart up to meet Christ in the air. If the word is used, it must keep the meaning of the original Greek word to mean departure from ones stand in faith and not taking off into the wild blue yonder.
I would also point out that, 'that Day' is not referring to 'the coming of our Lord and being gathered to Him' but to 'The Day of the Lord' found in verse 2 and also as 'that Day' in verse 3. Therefore, it is 'the Day of the Lord' that will not come until the apostasy occurs and the man of lawless ness is revealed.
The reason for the Thessalonians letter to Paul, which we don't see, is because there were false teachers there claiming that the Day of the Lord, the time of God's wrath, had already come. So since the Thessalonians knew Paul's teachings, that the gathering of the church would take place prior to the Day of the Lord, they were basically asking "He Paul, there are people here claiming that the day of the Lord has come, so why haven't we been caught up first as you taught us?" Of course Paul comforts them letting them know that the proof of being in the day of the Lord would be the apostasy and the revealing of the man of lawlessness, which had not happened and has yet to happen. It is not until after the church has been removed from the earth, the apostasy will have begun and the man of lawlessness has been revealed, as proof of being in the Day of the Lord. The Thessalonians were basically concerned that they missed the Lord's gathering and were now going to go through the time of God's wrath, the Day of the Lord.