It seems this program is at odds with itself. Longer life is jeopardizing the system and we have a program to increase the average life. The gubmint loses with either result. Sound familiar? I encourage everyone to live as good a life as possible. If smoking is a problem, the individual should quit. He does not need the gubmint to subsidize his desire.
It is very possible that stoping smoking may lead to a better quality of life that may translate into fewer drugs, operations, and healthcare visits, that more than offset the longer life.
It seems to me that even if the cost analysis is uncertain, that it's the right thing to do, given that Medicare is their insurance company.
Now whether Medicare charged a sufficient premium for the coverage provided, is a different question altogether.