filters on tables

On a 5.7 system, I overrode OnQuickSearchLoaded and enforced a 'Refinement' that restricted what records I wanted visible. 
There would be a Global variable that was set previously that I checked.

Refinements apply additional filters to searches.

It won't work against Global Search, that is definitely only limited by View Filters.
Is it really a problem if non-active employees appear in Global Search?

I don't have the code handy, but something like:

Sub OnQuickSearchLoaded(vntParam)
  
   Dim searchObj
   Set searchObj = UIMaster.RUICenter
   If (gActiveEmployeesOnly) Then
      Call searchObj.SetRefinement(0, True) ' This turns on Refinement #1
   End If

End Sub
     
Alternatively review your policy around assignment of activities to in-active employees, maybe re-assign to a 'Inactive Employee' employee record that is Active,
and record somewhere else who the original employee was...