A silent gallstone (i.e. one that is not causing any abdominal pain or biliary dyspepsia) measuring 1 cm in size can certainly be left alone without any need whatsoever for gall bladder removal. At your father's age the risks of surgery outweigh any benefits of gall bladder removal. The only silent gallstone that needs removal is one that is 3 cm or larger in size, due to the risk of malignancy in the gall bladder.