Food for thought: there are very very few bars in Chiang Mai that cater solely to farangs, there's one street in the centre that is slowly being closed down and then there's a smattering of farang bars spread over a wide area. There are of course places to drink but mostly they are entertainment venue's that combine food and/or live bands and tend to be upmarket-ish. There is, of course, the usual concentration of Thai oriented bars I suspect no more or less than anywhere else in Thailand.

Yet still, the tourist numbers here are quite high and by all accounts get better every year, it seems that tourists don't come to this neck of the woods for alcohol alone hence I don't think that closing the bars in Chiang Mai would affect tourist numbers more than by minuscule amounts. Of course, I agree that Pattaya as an example and Patong in Phuket are saturated with bars and banning alcohol would affect tourist numbers at those destinations, but over the medium term, would it!