If a student cancels their subscription, access to the course or bundle will be revoked when the next renewal or billing date occurs in Stripe and no payment is made. For example, if a student ends the subscription on Sept 1 and the next billing date is Sept 30, they will have access for 30 days and then lose access on Sept 30.
If you want to manually end a student's enrollment earlier, see How to Unenroll Students.