Split Excel file into multiple files based on number of rows

Try this on a copy of your workbook

Sub Maybe_This()
Dim j As Long
Application.ScreenUpdating = False
    For j = 1 To Sheets("sheet1").Cells.SpecialCells(11).Row Step 1000
        Sheets.Add , Sheets(Sheets.Count)
        Sheets("sheet1").Rows(j).Resize(1000).Copy Sheets(Sheets.Count).Cells(1)
    Next
    Sheets("sheet1").Cells.ClearContents    '<---- If you want Sheet1 cleared of contents
    Application.ScreenUpdating = True
End Sub