Certainly it is a cause for worry because bypass surgery is a palliative procedure and would last as long as you want it to last. If he resumes smoking and doesn't take care of the risk factors, then sooner rather than later, the blockages will come back. I therefore very strongly advise that you should contact your cardiologist, and may be a psychologist, who can bring about the behavioural changes necessary to stick to the recommended guidelines. For sure, smoking is an absolute disaster, what to talk of active smoking even passive smoking and standing to some one close by, who is smoking is harmful. Drinking alcohol beyond a particular limit damages heart, as well as liver but up to 30-60 ml per day may still be permissible as upper limits.