We filed the divorce paperwork but have decided not to go through it. What now?

If you ignore your divorce it will end. But in King County, ignoring the case scheduling order can result in sanctions. Better to write sign and file a Notice of Reconciliation telling the Court you both wish to non-suit the action. See CR 41.

You file a Motion and Order of Dismissal.

It depends on which county that you filed your case. Some counties will automatically dismiss your case if you do not show up for a trial assignment, while others may continue to track your case based on an internal case schedule. The best thing to do to make your case go away would be to enter an agreed order of dismissal so that you can be in compliance with the case schedule, no matter what county that you are in.