The park also lost power in 2010 during the 4th of July-ish timing.
The rides were evacuated following evacuation procedures.
As MarketingExpress stated, the rides do not have back up generators and will not complete their cycles.
Coasters will stop at the next breaking area if they are on the course at the time, flat rides will stop their cycle. Delirium would swing to a stop, from there, not sure how they would evacuate.
All water rides lose their pump power, so the water will drain and the flume,inner tube will stop at it's current position.