He should take it easy for the next 4 months at least. His sternum has to heal well before he could engage in any heavy work. We typically recommend about 4-6 months of recovery time after bypass.
He will not be permitted to do any lifting of more than 15 pounds until his sternum is fully healed. That is usually around 6 weeks. Everyone recovers at their own rate and you don't mention if he had heart attack, age or general health aside from his CAD. Certainly his physicians will be the ones to advise but with a good recovery (and otherwise good health), he hopefully will be able to return to his work. He may tire at first but will rebuild his stamina.
I am not a Doctor, but prediction is not something even a Doctor is going to necessarily be accurate on. There are many things to consider in order to answer your question. Firstly it depends on whether any heart damage occurred pre surgery. Second was the surgery a complete success. Thirdly will complications occur during recovery or further in the future. If there was no heart damage and the surgery was a good result, plus no complications occur during recovery then there is no reason why anyone cannot return to a normal life. However, if the job involves lifting, then I will be surprised if he will feel well enough after 6 months to do this. I had a triple bypass and my muscles took a year to recover fully.
A related discussion,
Heaviness in chest was started.