15% with treatment. The death rate from plague is about 50% without treatment. In the United States, with treatment, the death rate drops to about 15%. Most cases are bubonic plague. For pneumonic plague, the death rate is 100% without treatment. Pneumonic plague is a bad infection and is considered fatal if treatment is not started within 24 hours.
60-100% Pretty bad odds if not treated. 60-100% mortality reported. Even with treatment mortality is about 15%.