And I'm saying that shouldn't be how it always is, just because that is how it has been. Just because you are the PC, shouldn't be a magic shield against pissing off an assassin type character and reaping what you sow. If you do stupid evil things, being dealt with in your sleep or your drink poisoned, should be a possible consequence.
There is no "magic shield" (except when you activate a spell like that in combat, but that's a different story). Many characters, including the PC and companions are just stronger than that. A stealth dagger or poison isn't enough to kill them. Proof of that is is that there are enemy rogues that utilise poison or stealth in combat and can't kill you with one shot.
People forget that in a videogame the most important and unique storytelling device is the gameplay. What happens in battle isn't a separate dimension from the cutscenes and the story, it's the same. The fact that you overcome such trials in battle is why you don't get offed like that in your sleep. You really endure more. This is part of the character, it's an aspect of the story. Gameplay tells part of the story. A major part of it, in fact.
Not to mention that if you get killed in your sleep or by poison, enemy assassins would have done that ages ago. If you take an approach where PCs die like that, they wouldn't just die by doing bad deeds. They'd die by opposing the powerful antagonist who can hire assassins. Or simply by entering battle. Because the PC would be a weakling.
Once again, gameplay is a storytelling device, cutscenes and combat parts are not and should not be treated as different realities.