Just because the Holy Spirit’s restraint no longer prevents the rise of the Anti-Christ, that doesn’t mean the Christians have been taken out. It COULD mean that, but it doesn’t necessarily mean that.
It means that the restraining power of the Holy Spirit no longer restrains.
2 Th 2:7 7 For the mystery of lawlessness is already at work; only He who now restrains will do so until He is taken out of the way. (NKJV)
I’d recommend reading the Matthew Henry Commentaries on 2 Thess 2.