Is coronary heart disease reversible?

Unknwon. Although there have been suggestive studies that showed coronary plaque regression, most data is focused on plaque stabilization. As long as the plaque is stable and the symptoms controlled, it is not essential that we "revers" atherosclerosis. In the future, cetp modifying drugs may prove to reverse plaque. Only time will tell.
Depends. Since there are many causes, the answer depends on the cause. For example, if someone is born with a congenital anomaly, correcting the defect may correct the problem. However, if it is due to a multifactorial inflammatory atherosclerotic process then we may manage the disease, prevent progression - even achieve some regression- but we do not "cure" it.