During the initial encounter with Heorot, there is a seudo cutscene when he is dealt the fatal blow. It is possible to die during this cutscene if affected by a damaging status effect when it starts.
I had Aura of Decay active when the ‘fire god’ appeared and could passively watch as the damaged slowly ramped up during the locked encounter, until it became too much for my regen. Lucky for me it wasn’t a hardcore character.
Bonus bug: if you die after Heorot you respawn outside the ice wall that are supposed to prevent you from leaving, meaning you cannot get to Hearot.