Does a mitral valve repair last forever?

Not usually: It depends on the nature of the mitral valve abnormality and the type of repair. Since the mv is abnormal, it will probably not "age gracefully" and additional procedures may be required in the future. Lifelong cardiology follow up is important.

Depends: Depends on the age of the patient, previous pathology of the valve, final result after surgery, other medical conditions of the patient and so on. Typically repair is done for the mitral valve. In hands of a good surgeon, the right patient could have a very good, long lasting result. But as they say, nothing lasts forever!