Possible. Most colitis is treatable provided you don't let it go too far. Two types are particularly dangerous: ischemic colitis and c. Difficile colitis. Ulcerative colitis is particularly challenging but usually not immediately life threatening.
Its possible. Un treatred, rampant colitis can lead to serious bleeding and overwhelming infection either of which could cause death. This implies that the patient having the colitis totally ignores what is happening and simply lets the condition become deadly.