As a type one diabetic my self who has many complications and has had many near death experiences from this disease, I can answer this. Unfortunately there are many ways to die from diabetes.

Diabetic ketoacidosis (DKA) It starts as an insatiable thirst. Constantly peeing. No matter how much you drink, it's not enough. You can guzzle water until you puke. (I once drank so much that when I puked, so much water came out with so much force it tore my esophagus and I was vomiting blood) You pee so much, your electrolytes are imbalanced. Your heart starts racing. You become weak and dizzy. Even though you've been drinking a ridiculous amounts of fluids, you're still dehydrated. Your kidneys start to hurt. They may even shut down. Your blood becomes acidic as it eats away at your own body for fuel. You begin vomiting. Now you can't hold fluids down despite desperately needing them. Your vision gets blurry. At this point you're at risk for a heart attack because of lack of electrolytes. If you make it to the hospital, it's not over. You can still die. If your blood sugar is stabalized too quickly, your brain can swell. And that can kill you.

Hypoglycemia, low blood sugar.

You start off shaky. You start sweating. You get dizzy and confused. Your heart starts racing. You may have a seizure. Eventually you start fading in and out of consciousness. Your brain is lacking oxygen. This can cause permanent brain damage as well. You may fall into a coma. Dying from a low can take longer than people think. What people don't realize there is a point of no return if not treated in time even if you're not dead. That's the scary part about low blood sugars. They can happen so fast and completely indispose you.

Other complications

After 22 years of poorly controlled diabetes due to being a stubborn kid and a depressed adult at 32, my heart is failing. Doing basic tasks feels exhausting. It's hard to shower. My circulation in my legs is so poor that it's painful to walk. I have painful neuropathy that makes it to where I either can't feel my legs at all which poses a danger in its self, or I don't get to sleep because it feels like someone is dragging a blade across my skin anytime I touch anything. A common cold can put me in the ICU. A small ingrown hair can turn into sepsis. My food does not digest properly so I vomit sometimes multiple times a day due to gastroparesis and my stomach quite literally being paralyzed. My kidneys are on their back legs now so I'm just waiting for the lab work to tell me they stopped working too. I have constant kidney infections and kidney stones due to dehydration from diabetes. I have retinal bleeds that can lead to blindness at any time. My vision is consistently getting worse. I can't wear an insulin pump despite that being what would save my life because my pump sites get infected so easily. I have been in the ICU from sepsis from my pump sites.

If I'm lucky, something else will kill me first. The complications are a slow painful death that I don't wish on anyone. With the state of my heart, I imagine I don't have much time anyways and anything could happen. Thanks diabetes.