Except eveything you just said is completely false.
Dresden's mother's Death Curse was done to Wraith from many many miles away while she was dying from entropy curse/childbirth, so it sure doesn't require sight of the target. (If you bring up Changes, the reason he didn't use his death curse was because he didn't know who his killer was)
People's brains are still alive for betwee 7 and 20 seconds after death, and even if Eragon straight up chopped his brain in half, Dresden's soul would still be there for a few seconds before getting sucked off to the afterlife after the body's death just to make sure that Death curse hits.
And a death curse doesn't require speaking. Speaking spells in the Dresdenverse isn't like spells in the Potterverse, or even the Eragonverse. They are not conduits for magic, some mystical language that governs magic. "Feugo" is not "Brisingr". They are literally whatever word the wizard wants it to be, and different wizards use the same spells with the completely different words.
Dresdenverse spells are not words controlling the world. They are insulators for magic. Wizards cast spells in ancient languages that they do not understand, because the more they understand the language, the closer the magic comes to burning their minds, and the language of one's own thoughts is as just about as understandable as is possible for a person. Dresden dying would not care about keeping his brain intact, and would cast that spell straight from his thoughts.
Eragon's mind hax can be kept at bay simply by strong will and focus, and Dresden has more than enough of both. The man's contested his will against fallen angels, demons, Outsiders, high ranking Sidhe, vampiric gods, and he outwilled Demonreach and made it his butler, and that thing is basically the warden for a prison than contains mind-shatteringly horrifying demons in minimum security because everything past there is so much older, stronger and generally worse for humanity if it gets out. Eragon's mind hax gets lolnoped extremely hard.