In John 17:12, Jesus was speaking of His disciples. That was the whole context. But He excluded Judas from them and called him the son of perdition.
Joh_17:12 While I was with them in the world, I kept them in thy name: those that thou gavest me I have kept, and none of them is lost, but the
son of perdition; that the
scripture might be fulfilled.
When will the scripture be fulfilled?
Well, we are shown right here.
2Th_2:3 Let no man deceive you by any means:
for that day shall not come, except there come a falling away first,
and that man of sin be revealed, the son of perdition;
What day shall not come except.....?
2Th 2:1 Now we request you, brethren,
with regard to the coming of our Lord Jesus Christ and our gathering together to Him,
So the man of sin, the son of perdition, has to come before Christ returns, in which neither has happened.
The son of perdition is mentioned again, after Judas dies.. so we can rule him out, since its regarding a future prophecy, clearly..