بسم الله الرحمن الرحيم
Conditional talaq is like yamin (oath) (در مختار مع الشامى: 5:471 مطبوعه مكتبه زكريا ديوبند) and it is necessary to fulfil the oath and it may not be taken back. (حاشيه هدايه ثانى ص 323، حاشيه نمبر 9، 11 مطبوعه مكتبه اشرفيه ديوبند و در مختار مع الشامى، 5: 88-89). So the husband cannot terminate his oath and the three talaqs shall take place on his wife whenever he will smokes cigarette. However, there is an option by which the oath of three talaqs may be terminated. The option is that the husband gives only one talaq to his wife and smokes cigarette after iddah, thus the oath shall be terminated and three talaqs shall not take place, as a wife turns totally as a strange woman after iddah. Then And the husband will have to should marry her with new mahr again. And no talaq shall take place on the wife if he smokes after this new nikah as the oath was already fulfilled by smoking the cigarette after iddah and before the new nikah again. In this case, however, he shall have only the option right of only remaining talaqs not of three talaqs. But this option shall work only when the husband has not given two talaqs to his wife prior to this one. But And if he has given two talaqs before it then only one talaq is enough to turn the wife divorced with mughallazah (irrevocable) talaq. Hence if the matter is so then the husband should must abstain completely from smoking necessarily ; otherwise all the three talaqs shall take place due to smoking.
فحيلة من علق الثلاث بدخول الدار أن يطلقها واحدة ثم بعد العدة تدخلها فتنحل اليمين فينكحها هكذا فى الدر المختار(مع الرد 4:609).
Allah knows Best!
Darul Uloom Deoband