The Jesus wrote...
I've gotta agree take Waar's side here. However insomnia may affect you it can't directly lead to your death. Once you're body gets to a point where physically, it cannot take the fatigue from lack of sleep, I think scientists call it sleep debt, you'll just pass out. Sure being up for an extremely long period of time could cause you to die by inadvertently driving your car off the freeway into a ditch, fall out of a window, or die a wide variety of accidental, and sometimes extremely funny, ways. Regardless of how you die, the coroner's report would attribute it to the primary cause of death. I'm not sure it would mention the insomnia, unless it was absolutely necessary to clear up any questions as to whether it was an accident, murder, or suicide.
That was an example, when I was younger I suffered from insomnia and I almost died a few times from wandering around, trying to make myself fall asleep faster, and almost being hit by cars or falling asleep in places that were really dangerous for white, unathletic-looking people like me when I suffered from insomnia. The only reason I managed to get out of those situations was blind luck, and apparently sleep walking, which got me into as much danger as it got me out of, I think. The only times I would sleep walk was when I was already walking and would fall asleep which I am grateful for.
EDIT: Now to be honest the real killers in all of this are physiology and physics, or science, however you want to look at it.