Can one die from sleep apnea if untreated?

Yes: Sleep apnea leads to a variety of problems that can make a person die sooner than expected. Sleep apnea leads to issues such as: high blood pressure, heart disease, stroke, type 2 diabetes, metabolic syndrome, automobile accidents, etc... These issues sometimes are fatal, so sleep apnea should be treated. One's primary care doctor can help, and refer to specialists if needed.

Good Airway is very important and the most common problem of sleep apnea is obstructive. Not being able to breathe properly cannot oxygenate the whole body and can lead to serious diseases that can shorten life. The best treatment is preventive even from birth.

My colleagues have provided well focused answers, but I wished to add some caveats. Medication to treat pain, especially opioids, and sedative/ tranquilizers can cause apnea on their own at high dosing, and in presence of sleep apnea, the combination can become deadly.