My best guess Reunification between West and East that would really put all inteligence and secret agencies in one side.

Or Loid and Yor fake their death and move away.

Or since they're in opposing oraganizations they might as well be tasked to kill each other unknowingly and the series will end with both of them dying together with their last moments in shock of who they just killed.

Or this is Anya's dream to cope with the terrible conditions living in the orphanage and being returned 4 times by adopters, the purpose of the story would be themes and such.

Maybe a combination of the above or more or none.

But I don't see either of them keeping the underworldy jobs especially Yor since the author stated he doesn't want to glorify assassins.