É apenas uma questão simples de substituir a única referência da planilha por um loop externo adicional:
Sub abbrev()
Dim abvtab() As Variant
Dim ltsheet As Worksheet
Dim datasheet As Worksheet
Dim lt As Range
Dim i As Long
Set ltsheet = Sheets("sheet2")
' REFERENCE TO SINGLE WORKSHEET
' Set datasheet = Sheets("ACTIVE_DIRECTORY_User")
Set lt = ltsheet.Range("A2", ltsheet.Range("B2").End(xlDown))
abvtab = lt
For Each datasheet In Worksheets
If datasheet.Name <> ltsheet.Name Then
For i = 1 To UBound(abvtab)
datasheet.Cells.Replace What:=abvtab(i, 1), Replacement:=abvtab(i, 2), LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=True, SearchFormat:=False, _
ReplaceFormat:=False
Next i
End If
Next datasheet
End Sub
A planilha da tabela de consulta é excluída pelo nome.