In the present implementation, it is assumed that the parent and the child issue are in the same project.
In case this is not the case, the implementation has to be updated in order to retrieve the threshold value of the destination(see proposed implementation below). What do you think ?

for( $i = 0;$i < $t_relationship_count;$i++ ) {
        # verify if each bug in relation BUG_DEPENDANT is already marked as resolved
        if( $t_relationship[$i]->type == BUG_DEPENDANT ) {
            $t_dest_bug_id = $t_relationship[$i]->dest_bug_id;
            $t_status = bug_get_field( $t_dest_bug_id, 'status' );

            #  begin- Get the Project Id of the current child issue (set as destination)
                        $t_dest_bug_project_id = $t_relationship[$i]->dest_project_id;
            #  end- Get the Project Id of the current child issue (set as destination)

            #  begin - Check the bug_resolved_status_threshold of the child issue project (set as destination)
            #if( $t_status < config_get( 'bug_resolved_status_threshold' ) ) {
            if( $t_status < config_get( 'bug_resolved_status_threshold',null, null, $t_dest_bug_project_id) ) { 
            #  end - Check the bug_resolved_status_threshold of the child issue project (set as destination)
                # the bug is NOT marked as resolved/closed

                return false;
            }

        }
    }