Health care costs are not linearly related with age. The bulk of cost, at least in the US, are within the last six months of life, whenever you die.
Dying younger might save money if tobacco worked like the classic massive coronary at 50, where there were no symptoms to trigger medical care, it hits, and all EMS has to do is haul away the body.
The problem is that tobacco related deaths and other health exacerbations are generally a lobg, drawn out, and medically very expensive. COPD means decades of steadily increasing medical care needs, with lots of physician visits, specialists, oxygen, surgery and eventually debilitating hospitalization pre-death, all in a desperate bid to eak out a few more months of agony. Lung cancer has a shorter but more intense period of medical care and expenditure, as they desperately fight often metastatic cancer.
2015 estimates for direct medical care for smoking related medical needs is around 170 billion per year. Tobacco taxes brought in 25 billion. Estimates show a 10% relative reduction in the smoking prevalence will save something like 6 billion dollars in health care costs in the following year, though that focuses on mostly the reduction in cardiovascular and respiratory disease risks.