I’d do it something like this.
<?php if( have_rows('people') ): ?>
<?php while( have_rows('people') ): the_row();
// vars
$person = get_sub_field('person');
$person_url = get_sub_field('person_url');
if ($person_url) {
$person = '<a href="'.$person_url.'">'.$person.'</a>';
}
?>
<span class="person">
<?php echo $person; ?>
</span>
<?php endwhile; ?>
<?php endif; ?>