"before taking on the Quest “Find Ketheric Thorm’s Relic” as the Tieflings will die"
In practice, the lockout happens later - probably due to Balthazar fight.
I'm a bit pissed as I reloaded over 3 hours of exploring different areas, rescuing Roland etc.
Couldn't find the Tieflings in the prison as when I was inside the Prison, the map marker pointed at the stairs that were in the opposite direction, which meant leaving the area (didn't go far beyond the blood trails). So I read this article and since I already took on the quest, decided to replay that part to be able to complete the quest(s). It was totally unnecessary as I wasn't actually locked out.
