Exactly, the question with romanced Shadowheart is very interesting.
Also if you look at patch5 epilogs more detailed, you can see more and more plot holes with this update. If you imagine that Karlach is able to teleport instantly between Avernus and Faerun and has engine cooled down twice with infernal ores, she can spend quite a long time in Faerun. After the engine is going hot, she can basically teleport back to Avernus, spend a night in a tent and return back to Faerun and repeat this again and again.
