Right and Wrong, and why I think you are
I think that you are both right and wrong at the same time, but that's because there are two different things that need to be taken into account. One is that someone that partakes of risky behaviour is more likely to die off sooner, and thus in the long haul, cost the NHS less - This is where you're right. Where you're wrong however is in making the implied assumption that front loaded costs that are smaller overall is better than a more even spread of costs overall but cost more over a longer period of time.
If I offered you a loan and the pay back on the loan was either £200/month over 10 years or £100/month over 25 years which one would be cheaper? If you were looking at your monthly bills you might say the £100/month even though it will cost you £6000 more however you're saving £100/month. If you could afford the £200/month you'd probably say that that was the cheaper option as you'd be saving £6000 over all.