If you want to keep them all within one outer <li>, you can use something like this. Instead of echoing them immediately, save them to an array, then loop through the array.
<?php
if ($autores->have_posts()):
echo '<li>';
// create an empty array
$autoresArray = array();
while($autores->have_posts()): $autores->the_post();
// save the link and name
$autoreLink = get_permalink();
$autoreName = get_the_title();
// now add them to a multidimensional array
$autoresArray[] = array(
'link' => $autoreLink,
'name' => $autoreName,
);
endwhile;
// outside of 'while' so we only display the author list once
for($i=0; $i<count($autoresArray); $i++) {
// display the linked name
echo '<a href="' . $autoresArray[$i]['link'] . '">' . $autoresArray[$i]['name'] . '</a>';
// if it's not the last name in the array, add comma and space
if($i != (count($autoresArray)-1)) {
echo ', ';
}
}
echo '</li>';
endif;
?>