Allow limiting deletion of terms.

cms_modify_default_delete_term_caps.php

<?php

add_action( 'registered_taxonomy', 'cms_modify_default_delete_term_caps', 10, 3 );
function cms_modify_default_delete_term_caps( $taxonomy, $object_type, $args ) {
  global $wp_taxonomies;

	if ( 'category' == $taxonomy ) {
		$wp_taxonomies[ $taxonomy ]->cap->delete_terms = 'cms-delete-terms';
	}
}

add_filter('map_meta_cap', 'cms_map_meta_cap', 10, 4 );
function cms_map_meta_cap( $caps, $cap, $user_id, $args ) {
	switch ($cap) { 
		case 'cbs-delete-terms':
			$caps[] = 'do_not_allow';
			break;
	}
	return $caps; 
}