There are no large randomized controlled trials of comparing mortality between cigarettes usage and sleeping pills usage to conclude that sleeping pill use was associated with a comparable mortality hazard ratio as cigarette smoking which can be inferred when one goes through Daniel F. Kripke's review here. Also the available evidence of an association between hypnotics and mortality is not sufficiently strong and more independent studies are needed assessing the possible risks of hypnotics in order to give health care recommendations referring to Victor Vallejo-Garcia et.al. who declare no conflict of interest.
For absolute proof, we would need large randomized controlled trials of cigarettes or sleeping pills, but nobody is going to do such trials. How about the sleeping pill companies? Of course, now that we know that particular sleeping pills are associated with excess mortality, it would probably be unethical to do such a controlled trial, so for those particular sleeping pills, we will probably never have absolute proof whether they cause mortality or not.
The study on which Kripke had based his findings for sleeping pill use having a comparable mortality hazard ratio as cigarette smoking also had several other drawbacks listed below.
Concurrent psychiatric diagnoses were not addressed and so mortality may have been related more to suicide or substance abuse such as alcohol use.
Researchers were not able to conclude if the sleeping pills specifically contributed to the increase in mortality since in addition to risk of early death, participants taking sleeping pills had higher rates of asthma, cardiovascular disease, obesity and high blood pressure.
Associations seen in the study by Kripke et al. were heavily influenced by erroneous selection of the unexposed control cohorts referring to Anton Pottegård et.al. in 2014. Morten Andersen and Jesper Hallas, co-researchers in this mentioned point have participated in research projects funded by Nycomed, the manufacturer of nitrazepam, and Pfizer, the manufacturer of Halcion (triazolam) and Tafil (alprazolam), with grants paid to institutions where they have been employed. Dr. Kripke published the first controlled clinical trial of bright light treatment in 1981 and for the past 30 years has been doing research on light treatment and treating patients with light.
Limitations such as selection bias, overdiagnosis of cancer exist in the study and this makes it difficult to determine the specific contribution of hypnotics to mortality.