Dying from Mono is possible but very rarely does Mono become life threatening or cause death in the person who has Mono.
Death from Mono usually happens because of other complications such as a ruptured spleen so if you have a ruptured spleen it needs surgery right away before it gets too bad and cause death.
If you leave Mono untreated it can lead to inflammation of the liver and development of hepatitis.
So you need to get treated for the Mono if you do have it because it can become very serious.
If you have a ruptured spleen you'll have sharp pain in the abdomen which then needs immediate surgery to fix.