There are costs to individuals involved in every human action, but only a fool or a demagogue would pretend to be able to aggregate them in some mystical significant way. Businesses have widely varying policies for dealing with alcohol abuse, chronic absenteeism, and other personnel problems, ranging from immediate dismissal to theraputic sick leave. The managers of each business are best qualified to determine policy and take action they deem appropriate in each individual case. But again, you are assuming that ending prohibition will result in greatly increased drug use. Of course not.
Communities typically exercise control over the sale of alcohol, tobacco, and even gasoline.
Presumably, the situation with drugs would be no different. The government itself, through ill-conceived policies including the War on Drugs, has caused more family disintegration and child neglect than could possibly result from drug legalization. When cocaine and opiates were readily and legally available in the 19th century, this availability caused no epidemic of family disintegration. There was no sudden increase in alcohol consumption after the lifting of alcohol Prohibition. Government programs are notoriously wasteful and ineffective in dealing with alcohol abuse, while private organizations have a much better cure rate.