If it were that important, I would have a date field on the Customer with an Expiry Date for their latest Subscription. A User Event on the Subscription Record Type so that when it is saved, it updates the Linked Customer's Expiry Date field. When it's made inactive, it can set the Expiry Date to 1/1/1970 if needs be, or some arbitry date, but I would keep it so it was genuinely accurate, and search for Subscriptions Expiring On or Before Today...maybe even have a KPI called "Subscriptions Expiring within the next Month" 😉