Count the number of contiguous empty cells at the end of a row

I don't think there is any easy way to do this with existing Excel formulas. The problem is two-fold. First, AFAIK there is no Excel function that will tell you if a cell is part of a merged range. Second, the value shown in a merged ragne is actually only in the first cell of the merged range.

If you are willing to use VBA to create a custom function, this can be done fairly easily with a combination of the Match function and the fact that Range objects know if they are part of a merged range.

Public Function VLookupMerge(lookup_value As Variant, table_array As Range, col_index As Long) As Variant
   Dim sMatchFormula As String
   Dim row_index As Variant
   Dim r As Range

   sMatchFormula = "=MATCH(" & lookup_value _
                        & "," & table_array.Columns(1).Address(External:=True) _
                        & ",0)"
   row_index = Application.Evaluate(sMatchFormula)

   If TypeName(row_index) = "Error" Then
      VLookupMerge = row_index
   Else
      Set r = table_array.Cells(row_index, col_index)
      VLookupMerge = r.MergeArea.Range("A1")
      Set r = Nothing
   End If

End Function

You can do this using an array formula. Say The 50 columns of data are in columns A through AX, row 2 is your first data row, and the formula is going into AZ2:

    =50-MAX(IF(NOT(ISBLANK(A2:AX2)),COLUMN(A2:AX2),0))

The formula needs to be entered using Ctrl-Shift-Enter so it goes in as an array formula. Once it is entered, you can copy and paste 49 more copies down column AZ. The result will be the number of consecutive blanks at the end of each row (50 minus the column of the last non-blank entry). I tested it and it works.