I don't think you can take on this battle for him. He knows what needs to be done.

Better to be available for support, by remainng on good terms with him (which could otherwise become strained), if he decides to stop smoking.

CG to husband, dx @ age 65, nonsmoker/social drinker. Dx 5/08 SCC Stage IV, BOT T1N2aM0. 33 IMRT - completed 9/12/08. Induction Chemo (Cisplatin, Taxotere & 5FU), plus concurrent Cisplatin.
1/09 PEG removed; 5/09 neg PET/CT; 5/10 PET/CT NED
Dental extraction & HBOT 2013; ORN 2014; Debridement/Tissue Transfer & HBOT 2016