If the records were destroyed there may be ways of obtaining some or all of it by a roundabout method. Did you check to see if he filed a copy of his army separation papers (maybe DD214)with the county recorder? Did you check to see if he had dealings with the Veterans Administration such as GI Bill, loans or medical treatments. Any veterans benefit that was applied for would require proof of military service. Those types of records should still be in existance and obtainable.