We know you can create a user along with an entry. But when you delete the user entry the WordPress user remains, and vice versa. Here's some code that will eliminate a user's entries if you delete their WP user account, and if you delete the user account entry it will delete their WP account. NOTE: There is a frm_after_destroy_entry hook which would be preferable but it doesn't seem to work and FrmEntry::destroy() does a bunch of processing that sends it into an infinite loop. Also, if you try to delete a WP user with wp_delete_user() it times out, even if you include the WP script file. That's why why this snippet is written as such.

Specifying the $form1 (and optional $form2) will control which forms are appropriate.

// Delete user entries with user and vice versa
function my_frm_delete_user( $entry_id ) {
	$form1 = 1;
	$form2 = 2;
	global $wpdb;
	$frm_items = $wpdb->prefix . 'frm_items';
	$form = $wpdb->get_var("SELECT form_id FROM $frm_items WHERE id = '$entry_id'");
	if ( $form == $form1 || $form == $form2 ) {
		$user_id = $wpdb->get_var("SELECT user_id FROM $frm_items WHERE id = '$entry_id'");
		if ( !empty($user_id) ) {
			$users = $wpdb->prefix . 'users';
			$usermeta = $wpdb->prefix . 'usermeta';
			$wpdb->delete($users, array('ID' => $user_id));
			$umeta_ids = $wpdb->get_col("SELECT umeta_id FROM $usermeta WHERE user_id = '$user_id'");
			foreach ($umeta_ids as $umeta_id) {
				$wpdb->delete($usermeta, array('umeta_id' => $umeta_id));
			}
			$entradas = $wpdb->get_col("SELECT id FROM $frm_items WHERE user_id = '$user_id'");
			foreach ($entradas as $entrada) {
				if ( $entrada == $entry_id ) continue;
				$wpdb->delete($frm_items, array('id' => $entrada));
				$wpdb->delete($frm_item_metas, array('item_id' => $entrada));
			}
		}
	}
}
add_action( 'frm_before_destroy_entry', 'my_frm_delete_user', 10, 1 );

function my_wp_delete_user( $user_id ) {
	global $wpdb;
	$frm_items = $wpdb->prefix . 'frm_items';
	$entradas = $wpdb->get_col("SELECT id FROM $frm_items WHERE user_id = '$user_id'");
	foreach ($entradas as $entrada) {
		$wpdb->delete($frm_items, array('id' => $entrada));
		$wpdb->delete($frm_item_metas, array('item_id' => $entrada));
	}
}
add_action( 'delete_user', 'my_wp_delete_user' );