Based on the SF Bay Area experience of several years ago, you might see a slight drop off at the beginning of the ban, but let's face it, people don't go out to clubs and bars to smoke; they go to either:

a) listen to music, 
b) drink, 
c) hang out with friends, 
d) get laid
e) all of the above

Staying at home because you couldn't smoke didn't do much to meet those goals and people are plenty content to go outside to feed their habits, and it's made actually being inside a more tolerable experience, even for this long time smoker.  Everyone here waved the red flag too, but people adjusted pretty quickly. 

My 2 cents...
Steve