Could pulmonary edema be life threatening just by itself?

Yes: If the pulmonary edema is very severe the increased stiffness of the lungs ( which become log water logged sponges) and the fact that the air sacs are filled with fluid can cause respiratory failure. Depending on factors such as if the underlying cause can be corrected and how easy it is to support the patient temporarily with a mechanical ventilator, it may or may not be fatal.

Yes....: If the pulmonary edema is of rapid onset and is extensive, it could be life-threatening. If this diagnosis is suspected, an evaluation by a doctor is needed asap, perhaps even in the er if symptoms are severe.