Did he see a cardiologist or just a regular doctor? He needs to see a specialist because of an occlusion. He may need a couple of stents - which are not done open heart any more. EDTA treatment may open up those arteries without stents.... talk to a specialist.
Bypass surgery would be an option, but is not absolutely necessary. When the LAD is severely narrowed (greater than 70%) in the presence of blockage in the other arteries, then bypass surgery is the best option. However, your husband only has 50% narrowing in the LAD, so his options are broader.
The disease in D1, OM1, and OM2 can be managed with stents, or not at all. It depends on why he had the angiogram in the first place. If he is having symptoms (chest pain, shortness of breath, etc) then it would be reasonable to have stents placed. The big question is which vessel to stent first, and whether more than one vessel needs to be stented. If he is having symptoms, then he should have a stress test to see which area is causing the symptoms, and then fix that one. If he is not having symptoms, then there is no reason to fix the vessels -- it won't improve his outcome. We place stents in the setting of heart attacks or for symptom improvement, not just because there is blockage.