OK, you will have to explain that thinking a bit further for me - Jerusalem as a place obviously still existed. You cannot erase an area of the earth.
Perhaps you are saying that after the claimed destruction of the temple in what is generally said to be c.70AD(?), Christians would have been banned from that area by the Roman Rulers?
I don't see how an idea like that would be conclusive in thinking that Paul and the others could have met to talk in Jerusalem (despite any ban), or met to talk where some of them generally lived in the wider general area around Jerusalem.
But in in any case, since the copies that we have of Paul's letters were apparently written by Christians after about c.200AD, is it not obvious that they may have written about beliefs of Paul meeting principal members of the Jerusalem Christians 3 years and then 14 years after Paul’s visions?
Does Paul give a date? Afaik, he just says that after 3 and then 14 years, he went to Jerusalem to confer with the "pillars of the Church", he meant people (not stone pillars).
Why is it impossible for Paul go to Jerusalem to confer with Cephas and others at any time/date during his life... why does it have to be before a building was destroyed around c.70AD? That's apart from the fact that, as told 150 years after Paul had died, these may be entirely apocryphal stories of legend anyway.