5e actually has a death by my massive damage rule - not sure its used in BG3? I took huge damage (crit by by heavy hitters) and I am sure this rule should have kicked in, but I was just unconscious.
"Instant Death
Massive damage can kill you instantly. When damage reduces you to 0 hit points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum. "
For a low hp wizard - at lower levels - this can be easy to reach with a crit (especially from sneak attack etc)
Also, a hit when you are at 0 hp should be a failed death save, and a crit is 2. 3 failed death saves = death. I did have some characters die when they were down in honor mode and the AI relentlessly went after them - definitely adds
tension...
That said, 5e is much more tolerant of getting hit down to 0 - older versions you just died.
