Would healthcare costs increase (in the long term) if all smokers quit? According to research by Jan J. Barendregt, M.A., Luc Bonneux, M.D., and Paul J. van der Maas, Ph.D.:


  RESULTS
  
  Health care costs for smokers at a given age are as much as 40 percent higher than those for nonsmokers, but in a population in which no one smoked the costs would be 7 percent higher among men and 4 percent higher among women than the costs in the current mixed population of smokers and nonsmokers. If all smokers quit, health care costs would be lower at first, but after 15 years they would become higher than at present. In the long term, complete smoking cessation would produce a net increase in health care costs, but it could still be seen as economically favorable under reasonable assumptions of discount rate and evaluation period.


When it comes to short-term effects, Cancer.org claims that:


  
  From 2000 to 2012, tobacco-related health costs and productivity loss in the United States totaled $289 Billion
  The average price of a pack of cigarettes in the United States is \$6.36. But each pack of cigarettes creates $35 dollars of health-related costs for the smoker.
  


However no information is given on long-term effects.

The question is therefore: if everyone stopped smoking, would healthcare systems around the world see a net increase or decrease in expenses in the long term?
It is a reputable journal and the results are surely correct on a "total dollars" sense. I guess the point they are making is that because health care expenditure of old age individuals is very likely to be high, there is some 'social benefit' of dying before old age. 

However, it seems somewhat meaningless: 

A) First, by this logic, murders also decrease health care costs. We're not trying to keep smokers form smoking solely because they will be a health care burden. We also want these people to live long, rewarding lives.

B) People contribute to society, their families, their friends and so on. They also save and, specifically, they pay health insurance premiums while they are alive. So, while they might require more care in the long run, non-smokers might well be able to pay or it with the taxes on their income and the productivity they bring to society. Similarly, we all invest through our taxes, on public education, and it goes to waste when somebody that has received public education dies.

C) There are enormous variations in the amount of healthcare spending that old people receive across countries, so the estimates of how much health are old people will receive has got to be very imprecise. 

D) Investments pay a positive rate of return, so if we saved the money now we could pay for a lot more care later. Put differently, all the resources that would not be devoted to the care of smokers now would be used to improve our lives meaningfully, potentially even helping us do research into how to take care of old people effectively, which would again reduce the future expected cost of caring for the smokers.