Encouraging smoking to save money is an unethical thought experiment not actual policy. Smoking is not guaranteed to kill and due to modern treatments it is a lot more survivable now. This means it will be significantly more expensive if people smoke. Quality of life is also significantly reduced along with productivity.

Kids are not required by law to take care of their parents so you can't count on that. Besides, most of the really high costs are from living in a care facility. Most people cannot provide this level of care.