I used to smoke, but have not had one since this beast tapped me on the shoulder. While we can never be certain what causes our individual cases, smoking is a known contributor. Also, any surgeon will tell you that smoking adversely impacts recovery time from surgery. Any patient going through this treatment needs to have every possible thing going for them, and continuing to smoke is, simply stated, suicidal.
You can't control whether he stops or not, but do your best to have the doctors tell him point blank the likely impact of his continuing to smoke. Hopefully that will do it. I did not need to be told twice!