Would someone with mild atelectasis need to be hospitalized?

Not usually: Atelectasis alone would most often not require hosptializatoin . Atelectasis is a symptom/sign of many types of lung diseases/illnesses. The other parts of the illness may be more serious than the atelectasis, such as trouble breathing , hypoxia (low oxygen), cardiac complications, etc.

No...: Mild atelectasis, especially without symptoms, can be treated as an outpatient. The most important treatment is deep breathing and an incentive spirometer can help with this. Ask your doctor for one if you don't have one. Good luck!