Sometimes. Sometimes pneumonia is a simple viral process that self heals. It can also be an aggressive bacteria that invades the body starting with the lungs and can kill within days if not discovered and treated. Jim Henson, the puppet master that created the MUPPETS did not get treated for his pneumonia until it was too late, and died because of it.
Possible. Pneumonia can be a life-threatening problem especially if left untreated. You should see a doctor if you are having symptoms of pneumonia.
Yes. But this depends upon the underlying health status of the patient, the causative organism, time and efficacy of therapy and other factors.