Is it possible a collapsed lung will heal without a chest tube?

Yes: A collapsed lung is due to an air leak from the inside of the lung through the covering of the lung, out into the space between the lung and the ribs. The site of the leak has some damage, which will heal itself later. If only a very small amount of air leaked into the chest cavity, that air can go away without treatment. If a little more air leaked, a doctor can suck the air out with a catheter.

In some cases, yes: A small pneumothorax will resolve without any treatment. It's a judgment call for the physician to decide (depending on the circumstances) when a pneumothorax is large enough to warrant the placement of a chest tube. Factors to consider include: size of the pneumothorax, the cause, the severity of symptoms, and other medical conditions.

Only if very small: Only if very small, and does not get bigger with serial cxr. Air in the pleural space (pneumothorax) gets smaller by 1% every day if the lung is not actively leaking.

Possibly: The treatment for collapsed lung (pneumothorax) can range for simple observation to surgical treatment. The type of treatment used is determined by a number of factors: size of pneumothorax, likelihood of resolution, likelihood of recurrence, cause and symptoms, A small assymptomatic pneumothorax may be observed. A tension pneumothorax can be life threatening and requires immediate treatment.

Yes: If the pneumothorax is small, it is possible to not need a chest tube. Using 100% oxygen will help absorb the air and potentially keep someone from need a chest tube.