The effect on an organism of an injured or diseased kidney depends on the extent and severity of the damage. The kidneys play an important role in filtering out waste from the blood. If they can't do that well enough, waste builds up to the point where people can get sick and even die.
If part of the kidney were injured or diseased, metabolites will accumulate. There will be a lessening of the creation of erythropoietin, which is needed to force the long bones to create red blood cells, necessitating the intake of epoetin alfa (Epogen, for example) to artificially stimulate red blood cell generation along with iron supplementation. This damage may also restrict the elimination of urine, causing the organism to start "poisoning" itself. In humans (and some animals), this necessitates the need for dialysis.