The easiest way to approach this given the code you have provided is to reverse the order of your code. Do the foreach before the title, and instead of outputting the post content using echo, append to a variable. Then check if the variable has anything to output and if so, output the title.
$post = $post_objects;
setup_postdata($post);
# create variable collect content
$content="";
foreach ($post_objects as $post):
setup_postdata($post);
if (is_object_in_term($post->ID, 'tshowcase-taxonomy', Assistence)) {
if (has_post_thumbnail()) {
# append content to $content variable
$content .= '<a href="' . get_permalink() . '">' . get_the_title() . "<br>" . get_the_post_thumbnail($postid, array(150, 150), array()) . '</a><br>';
} else {
# append content to $content variable
$content .= '<a href="' . get_permalink() . '">' . get_the_title() . '</a><br>';
}
}
endforeach;
# check if $content variable has content
if( $content != '' ) {
echo '<h4><i>' . Assistence . '</i></h4>';
echo $content;
echo '<br>';
}else{
echo 'empty';
}
wp_reset_postdata();