The most dangerous type of diabetes ...is they type where you dont control your BG numbers.
left * uncontrolled * both types can kill. Some think eating healthy (low glycemic carbs) and exercise can help prevent or delay T2 There is no way to prevent T1. T1 is a disease where you body thing the insulin producing cells in your pancreas are invading. so your immune system KILLS your insulin producing cells.
T1s MUST use insulin or die.
T2s can use pills and or insulin too.
Diabetes is a difficult thing in regards to what it affects in the body and what affects it. So many things are complicated by diabetes. Anything having to do with the circulatory system could be compromised by diabetes. Heart, liver, kidney disease is all complicated by diabetes. Thyroid function is often affected by diabetes and that runs the other way too. Thyroid function can affect diabetes.
You appear to be a bit confused on Type 1 and Type 2. Type 1 is not the only type treated by insulin. Google it for a could of good reads. It would be better than me trying to explain it here.
Diabetes can be genetic. When doing an annual check up with your doctor, make sure you are getting a thorough blood screening done and make sure you are getting an hbA1c.
People with diabetes do often live normal, long and relatively healthy lives. It has a lot to do with the attention you pay to it, time of diagnosis and what you do to prevent the disease furthering in your body.