How many million lives could we save in the us if we all stop smoking?

About 600,000 yearly. Smoking causes lung cancer at about 500, 000 deaths per year plus chronic lung disease, heart disease, bladder cancer and a host of other problems (let alone smilling up the place). If stopped, over time, there would probably average out about 600 k per year but it would take a while for the accumulated damage to be eliminated. If you are smoking - stop.