PMPro snippet to disable the "Cancel" button when the auto-renew option is turned off.

pmpro-conpd-avoid-complete-cancellation.php

<?php
/**
 * Remove "Cancel" button for cancelled subscriptions.
 *
 * The user is still able to cancel auto-renew, but can't completely cancel the membership.
 */
add_filter( 'pmpro_member_action_links', function ( $pmpro_member_action_links ) {
	global $current_user;

	// bail if cancel link has been removed by someone else
	if ( ! isset( $pmpro_member_action_links['cancel'] ) ) {
		return $pmpro_member_action_links;
	}

	// get current user level
	$level = pmpro_getMembershipLevelForUser( $current_user->ID );

	// bail if not a recurring level
	if ( ! pmpro_isLevelRecurring( $level ) ) {
		return $pmpro_member_action_links;
	}

	$morder = new MemberOrder();
	// guess the order which triggered the current user level
	// TODO use subs table to define if the subs is still active.
	// atm there's no way to know if a refunded order is for an active sub at gateway.
	// it's better to assume that only orders in status "success" are still active at gateway.
	$morder->getLastMemberOrder( $current_user->ID, 'success', $level->id );

	// consider paid recurring orders without an enddate
	if ( ! empty( $morder->id ) && ! empty( $morder->subscription_transaction_id ) && ! empty( $morder->enddate ) ) {
		unset( $pmpro_member_action_links['cancel'] );
	}

	return $pmpro_member_action_links;
} );