Can you die of kidney failure?

Not neccesarily. Mild kidney failure does not. Severe kidney failure can be correctable also. Otherwise severe damage is treated with dialysis and transplantation. Chances of death increase with severity.
Yes. Untreated renal failure results in the build up of toxic chemicals in the blood which have a multitude of negative effects on all organ systems. Fortunately some forms of renal failure can be treated and when untreatable, dialysis can result in significant benefits.