Without a doubt traffic elsewhere will increase whether or not it decreases here but I am sure theymos already factored in that possibility in when he made the decision to ban mixers.
I think those that do end up using that forum or another will not give up here because the campaign payments here are higher. They would rather use more than one forum than be restricted to just one if it means making more money.
This is not to criticize theymos' decision to ban mixers, which I understand in order to prevent greater evils in the future, but it is important to be aware of the danger of traffic transfer if further restrictions are introduced in the future.