So I'm maintaining a database that stores employee info. When an employee leaves there info no longer needs to show up in many of the forms/reports etc.

However some reports and such refer back to the past when that employee was still there (the Employee ID is still referenced)

Up till now they have been deleting old records and losing all that data, but now they want to move that data to a separate table to Archive it.

I have a VB script to do this, but I'm wondering would it be more efficient to make a Yes/No field for Active/Inactive and then use a simple filter for all my other objects rather than the union query I have now to join Current and Archived Records

... make a Yes/No field for Active/Inactive and then use a simple filter for all my other objects

That would be my choice.

You wondered correctly. I would use a status field and simply filter them out as appropriate.