Smoking effects some voices more than others. Decades of heavy smoking can certainly darken the tone somewhat and for some singers cause them to lose range, but then there are singers like Sarah Vaughan, who still had one of the most extraordinarily beautiful instruments of the 20th century at the time of her death. While her timbre was a bit darker at the end (which was also in part due to the fact that she was in her mid 60s and voices typically get heavier as one ages), she still had three+ octaves of range and could still famously hold a note, perfectly on pitch with vibrato for 30 seconds (she actually did it once on a dare on a tv special in the 80s, shortly before her death -- 32 seconds I believe).
I don't know. While it's certainly not good for the voice or overall health, smoking effects different people in different ways (genetics play a huge role), so don't freak if you find out your favorite singer smokes. MANY of the greatest singers in history were smokers at one time or another (I have a theory that it comes from the fact that most singers are orally-fixated) and a surprising number of them kept their voices in tact for decades.
"What a story........ everything but the bloodhounds snappin' at her rear end." -- Birdie
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"The Devil Be Hittin' Me" -- Whitney