Jaanika,
Please go to this blog site and read it carefully and look at the pictures. Try to show it to your father.
Rich's PleaThis is what happens if he continues to smoke after being diagnosed with oral cancer. It will probably recur.
In the US there are nicotine replacements (patches, gum, mints) that help some with nicotine withdrawal. Nicotine is not one of the carcinogens found in cigarettes, but it is the addictive substance that must be dealt with. There are also prescription drugs available here through a doctor such as Chantix which may give him the support he needs to stop smoking.
BUT...HE MUST STOP SMOKING! Drinking is a secondary concern.
HE CAN DO IT!!! Many people here have.
Best of luck in helping your father.