Do you have to treat walking pneumonia? if recovered without treatment, does it leave permanent scarring in the lungs?

In a way: In a way, you need to treat of course, as if it was viral (your probable case since you recovered without antibiotics) you would rest and push fluids and treat it supportively. If bacterial, you would need antibiotics. Usually, the body will heal itself, but on a rare occasion, you may leave some scarring from an old infection.

Treat Symptoms: If you have fully recovered and have no symptoms there would be no sense in treatment. Many winter illnesses are viral in nature and one clears these on their own.