The police officers that were shot were NOT Ferguson Police officers. They were St. Louis City Police and Sheriff Department employees.
The police department in Ferguson does not need to walk away. They are all going to be fired and replaced by County Sheriffs. The City will simply contract their police services to the Sheriff's department and these officers will all be out of a job - unless they can hire on with the Sheriff's department.
Why any law enforcement AT ALL would choose to work there is beyond me.