If I understand you correctly, you have a two row table in the mailmerge
main document.  To do what you want, you need to select the first row of
that table and then format the paragraph so that it is kept with next.  Then
you need to select the second row of the table and in the Table>Properties
dialog, (Table Tools>Layout>Properties>Rows) uncheck the box against "Allow
row to break across pages".