Motorsport advertising doesn't bring in new smokers. New smokers are created through cultural images or social interaction, not through advertising. You smoke to look cool, and you'll only look cool if you have someone to look cool in front of.
For roughly two decades, I've watched cars sponsored by John Player Special, Marlboro, Benson-Hedges, Mild Seven, Rothmans, Lucky Strikes, Camel, Silk Cut, Skoal, Winston, Copenhagen, 555, and a plethora of other brands. That was during all my "young and impressionable" years. And y'know what? I never once had the desire to smoke. Well, not tobacco, at least. None of the drivers smoked, and those were the guys I wanted to be like! Plus the liveries were often distinctive and beautiful (especially Rothmans and JPS).
Those of you who think other industries will step up to fill the void... Nope. Not gonna happen. There might be _just_enough_ money coming from them to keep the sport alive, but that tobacco money's gone forever. It was a huge amount of money, spread around everywhere from karts to F1 to WRC to motocross... Tobacco sponsorship pretty much made this sport widespread and accessible!
The whole tech sector of the British economy... Hell, of the AMERICAN economy, even... Will never have as much money simply to throw around in advertising as Phillip Morris alone. The tobacco industry had very little overhead, couldn't advertise on TV, and made insane profits from selling to addicts. They really had very few places to put all that money, so they just heaved huge sacks of it at sports.
Without that money, the sport will never look or feel the same.
Sorry.