Some questions that may need to be considered...
Do the after hours traffic movements warrant an approach service?
Is industry happy paying for an approach service for only a handful of movements per evening?
What is the problem we are trying to solve through the running of an approach service? What does the approach service actually provide vs not having it?
What is the current airspace risk level? and what will it be when the approach service is removed? Can other things be implemented to mitigate this risk?