In the absence of screening and treatment of diabetes, what are the risks?

In the absence of screening and treatment of diabetes, the main risk is that the disease is revealed by a complication.

It is more often a complication of vascular order (coronary insufficiency, myocardial infarction, stroke, arthritis of the lower limbs).

It could also reach the small vessels, the retina with a decline in visual acuity, renal damage with emergence of albumin in the urine, and then renal insufficiency (diabetes becomes the first cause of end stage renal disease).

It may occur a nerve damage (neuropathy), of an accident such as a facial paralysis. In addition, in the case of a neuropathy with disorder of peripheral nerves, appear signs of glue polyneuritis over and a burning sensation under the feet or the impression of walking in the cotton.
Eventually, acute complications are favored by a diabetes unbalanced and therefore undiagnosed. It can be for example an infection from a wound which heal properly.

Diabetes is an insidious disease, the objective is therefore an early diagnosis to avoid the risk of complications, or even a diagnosis to the stage of pre-diabetes can to treat by hygieno-dietatry measures  even before the diabetes appears.
See also Diabetes symptoms, how to detect them early