Sub UnMergeFill(ByVal ws As Worksheet)

Dim cell As Range, joinedCells As Range

For Each cell In ws.UsedRange
    If cell.MergeCells Then
        Set joinedCells = cell.MergeArea
        cell.MergeCells = False
        joinedCells.Value = cell.Value
    End If
Next

End Sub

sub UnMergeFillAllSheets()
    Dim ws As Worksheet
    for Each ws In Worksheets
         UnMergeFill ws
    Next
End Sub