Insulin increase leads to an increase in the sodium to be taken up by the cell. So, low sodium means low insulin secretion.
Too less of sodium in the blood (below 135 mEq/L) leads to increased water absorption by the cells and decreased blood volume. The blood volume decreases to such an extent that the pressure becomes too low to even be conveyed to the heart. As a result, the heart muscles try to exert extra strain to pump the blood.
Cholesterol issues: Low sodium leads to lesser blood volume and this intensifies the effect of the bad cholesterol in your body.
Increased mortality risk for diabetics: Here too low sodium levels in the body leads to more insulin resistance or insulin inactivity. This result along with the heart failure and cholesterol intensification aspects put together, increase the death risk in a diabetic individual.