In truth, Davis thought of letting Vereina out in a month or so. After all, his disguise as Feng Chu was going to be known to all pretty much soon anyway. It was just... if he could prolong it, why not?
That was the sole reason he wanted to keep Vereina here.
As for whether Mo Tian or Dead End would be exposed if Vereina were to reveal the fact that he hadn't just ascended like yesterday, that really was complicated as Vereina was a Divergent herself. No one would take her word for it but try to kill her if she revealed herself outside.
But now, it could be said that he managed to make an acquaintance with a Divergent, and the other party truly was of the intent to forgive and forget from what he could tell. At least, on the surface, it moved in that direction with the other party trying to be sincere, so he rather hoped that it wouldn't turn hostile and, consequently, disappointing.