1) interesting. I didn’t try killing any companions in 1.0, but I remember Astarion annoyingly refusing to die for good in EA. Entering mountain area makes you enter act2. I wonder if Laez body was teleported there as a form of “progression” - removing her from act1 area and moving her into act2. In 1.0 you can still return to grove area after progressing, but perhaps, it wasn’t always meant to be so, and that was a way to not prevent players from resurrecting dead companions if they wished to do so. Clunky, but BG3 doesn’t quite like taking no for an answer.
As to dragon - I am pretty sure it is real - he was even possible to kill him in EA. He should leave in a cutscene when you approach Gith. You just broke it

2) As you might have gathered [spoiler]the artifact is plot critical. If you don’t have Shadowheart with you, or you kill her artifact will land with you. The game gets confused about it - and eventually decides that you had the artifact all along. I was surprised to see it - Larian has been so concerned with handling artifact if you don’t encounter Shadowheart, that it seems they forgot to check progression when you DO have Shadowheart with you at all times.