Place a PMPro member in another level when they cancel.

pmpro_cancelled_level.php

/*
	When users cancel (are changed to membership level 0) we give them another "cancelled" level. Can be used to downgrade someone to a free level when they cancel.
*/
function pmpro_after_change_membership_level_default_level($level_id, $user_id)
{
	//if we see this global set, then another gist is planning to give the user their level back
	global $pmpro_next_payment_timestamp;
	if(!empty($pmpro_next_payment_timestamp))
		return;
	
	if($level_id == 0) {
		//cancelling, give them level 1 instead
		pmpro_changeMembershipLevel(1, $user_id);
	}
}
add_action("pmpro_after_change_membership_level", "pmpro_after_change_membership_level_default_level", 10, 2);