Basically you need to compare the date it is now with the end date. This is not exact but how I might do it. Hopefully it point you in the right direction.
while ( have_rows('t_block') ) : the_row();
$now = strtotime(date('Y-m-d', time()));
// I am assuming that your date is stored as 'Y-m-d'
// see strtotime php doc form more information
$end_time - strtotime(get_sub_field('ende'));
if ($now > $end_time) {
// not in the future, go to the next row
continue;
}
// the rest of your code here ...