I had modified the code initially done by Graham.

1. Code will split for all columns
2. Split cells will contain previous merged cell value (Graham code even replaced previously empty cell, now the bug is squashed)
3. Added comments where ever possible for easier understanding of what each block does

In my opinion, i can do the same work in C#.Net Word VSTO Addin in less than an hour with the help of full fledged OOPS language, rather than writing huge boilerplate code just to split cells in table with vba.

Function SplitVerticalMerge()
    'Created by Chandraprakash [Yoh]
    Dim i As Long, j As Long, k As Long, cols As Long, m As Long
    Dim sData() As Variant
    Dim oTable As Table
    Dim oCell As Cell
    Dim oRng As Range
    Dim sText As String
    Dim sRow As String
    Dim iRow As Long
    
    'Rows of Merged and NonMerged cells in Table
    Dim oColl1 As New Collection
    
    'Row with number of merged cells in Table (Vertical Split Number)
    Dim oColl2 As New Collection
        
    Set oTable = ActiveDocument.Tables(1)
    With oTable
        
        'Load all the Table cell index
        ReDim sData(1 To .Rows.Count, 1 To .Columns.Count)
        Set oCell = .Cell(1, 1)
        Do While Not oCell Is Nothing
            sData(oCell.RowIndex, oCell.ColumnIndex) = oCell.RowIndex & "," & oCell.ColumnIndex
            Set oCell = oCell.Next
        Loop
        
        '1. Mark the merged cell as "X"
        '2. Mark the non merged cell as "A"
        '3. Load the result for each row to Collection1
        For i = 1 To UBound(sData)
            sRow = ""
            For j = 1 To UBound(sData, 2)
                sRow = sRow & IIf(IsEmpty(sData(i, j)), "X", "A") ' & "|"
            Next j
            oColl1.Add sRow
        Next i
        
        For cols = 1 To oTable.Columns.Count
            'Load one by one Row with number of merged cells in Table (Vertical Split Number)
            Set oColl2 = Nothing
            j = 1
            For i = oColl1.Count To 1 Step -1
                '"X" - Merged
                If Mid(oColl1(i), cols, 1) = "X" Then
                    j = j + 1
                    k = j
                '"A" - NotMerged
                Else
                    k = j
                    j = 1
                End If
                If j = 1 Then oColl2.Add k
            Next i
            
            iRow = oTable.Columns(cols).Cells.Count
            k = iRow
            For j = 1 To oColl2.Count
                For i = oColl2.Count To 1 Step -iRow
                    'cols - Column Number
                    'k - cell row number in column (cols)
                    'j - Split number for the cell (k)
                    
                    'Split the cell by above attributes defined
                    oTable.Columns(cols).Cells(k).Split oColl2(j), 1
                    
                    '1. Enter if merged cell is split (j>1)
                    '2. Will fill the values for split empty cell with previous merged cell value
                    If oColl2(j) > 1 Then
                        For m = 1 To oColl2(j) - 1
                            oTable.Columns(cols).Cells(k + m).Range.Text = oTable.Columns(cols).Cells(k).Range.Text
                        Next m
                    End If
                    
                    k = k - 1
                Next i
            Next j
        Next cols
        
        'To avoid application freezing
        DoEvents
    End With


lbl_Exit:
    Set oColl1 = Nothing
    Set oColl2 = Nothing
    
    Set oTable = Nothing
    Set oCell = Nothing
    Set oRng = Nothing
    Exit Function
End Function