The player character does not have immunity to "Instadeath"?

[Kalirion]

My berserker was surrounded by "internal demons" clones, and was low on health, so I switched on "Unstoppable" which was maxed at the time. Killed 3 or 4 critters while under it, when unstoppable ended I should have had a large chunk of the 1500 max health. Instead, around the time it ended I was dead.

Took a look at the game log - about that same time one of my clones performed Death Blow. With the armor and physical resistance I had, the crit should not have done more than 200-300 damage or so tops, so I'm guessing it was the instadeath that killed me.

[Grey]

Were you playing in Insane mode? Insane difficulty strips the character of "Elite" status, which then makes insta-death possible.

[edge2054]

The player is not instadeath immune. While many instant death effects check for rank the two effects are not dependent on each other.

[Dervic]

There are a few nasty spell effects that prevent Unstoppable Healing (Blood Lock, Impending Doom). I'm thinking you didn't get healed when Unstoppable ended but I can't be sure without logs.

[edge2054]

There's also a disease which can remove Unstoppable. It's not a 100% fool proof effect (nor should it be).

That said I just double checked and the player is in no means instakill immune. If he was it would be on the character sheet (I gave a test character instakill immunity and it shows up).

But maybe unstoppable should make you instakill immune. Every instadeath effect I know of checks if your hit points are low which means you're very vulnerable to instakills with unstoppable going.