Usually not, but... Once you stop smoking, the destruction from the smoking stops. But, the decline in lung function does not. Everyone loses lung function with aging. But those who have COPD may lose that function at a faster rate, even if they stop smoking. Does that mean they should continue to smoke? No!
Yes, but... Although the changes of emphysema and COPD are generally irreversible, the rate of decline of lung function is less when you stop smoking compared to when you are smoking. In addition smoking cessation is recommended because it reduces the risk of death from other smoking-related conditions such as heart attacks and strokes and many cancers.
Yes... Emphysema, a form of copd, is a slowly progressive disease that has no cure. Smoking cessation slows the progression of disease but doesn't stop disease progression. If your oxygen level is low enough, supplemental oxygen is prescribed and this helps to decreases morbidity and mortality rates. Smoking cessation also decreases your risk of lung cancer. See your doctor so treatment can be initiated.