If someone's been smoking for 25 years, can their smokers cough disappear if they stop smoking?

Yes. It may take a few moths but a smokers cough can improve or resolve after you stop smoking.
Cough. Commonly, after someone quits smoking, they continue to experience a cough for 4-6 weeks after quitting. After this period of time, the cough seems to improve. If you are still coughing after quitting smoking for 6 weeks, it may be something else. With 25 years of smoking, bronchial problems are a possibility and could result in coughing too.