Your ifs are wrong.
But it's a good idea to ban it everywhere? At least you point out that this is not a guaranteed outcome.
I am explicitly not saying whether it is a good idea to ban it everywhere. Because I don't know enough about the specifics of England to say whether I think it is.
In California it clearly has been good. The ban was implemented, it is very popular, people are going out and eating more, smoking is down - it is hard to find a significant downside. Even most smokers that I know are for it. (Of course smoking outside is not a problem for them in Southern California because it never gets very cold.)
In England it might not be good, I don't know.
IF more smokers come out, then there is an unmet demand. If there is demand, money can be made supplying it. Unless the demand is insufficient to support the business. If demand is insufficient to support the business, then it's a case of a group forcing their choices on others.
LEARN SOME FUCKING ECONOMICS, PLEASE!
It is common with public goods that there is unmet demand and one simply cannot make money trying to meet it in the obvious way. All that I am trying to do is point this out to you. If people expect bars to be smoky places, many non-smokers will not go to bars. And there is no way for a single bar to get past the immediate assumption to communicate that they're really different.
The result is that private attempts to do what most people want done frequently fail. And their failure says little to nothing about how much untapped desire there is out there.
In such situations there is often a choice between not allocating the public good, or allocating it by coercion. Sometimes allocating it by coercion is a good idea. (Personally I like having a highway system.) Sometimes allocating it by coercion is a bad idea. (I dislike what we're doing in Iraq.) But it isn't as simple as telling people, "If you're not doing it on your own, then you can't really want it."
Cheers,
Ben