I asked this question yesterday, and if a decision has been made, it hasn't gotten down to the level of supervisors yet.
I suspect, though, that they'll do what they have in the past with their fireworks... used them uniformly throughout the summer and then only use them at busy (late closing) times of the year. They spent a lot of money putting the infrastructure in place for Mystify, so I can't imagine they would just stop using it entirely.