Alcohol, in large quantities is a risk factor for oral cancer. But all things are relative. You haven't mentioned how many years he drank or how many drinks per day. What would appear to be excess, is perhaps not medically excess. So I guess what I am saying is that from your post it is hard to tell if it was a contributing factor to the first occurrence of OC. Non smokers also get oral cancer from viruses and other sources. An occasional drink after this process is usually not forbidden by most doctors, though most patients cannot tolerate the burn that goes along with it, or if they have xerostomia, the exacerbation of the already dry oral tissues by alcohol. If it concerns you, I suggest that you speak with the doctor about what he considers allowable. That conversation may belay your fears, or prompt a doctor patient conversation if necessary.