They remain yours. You will continue to have access to previous course and bundle purchases after you've subscribed to A Cloud Guru Memberships.
At any point that you decide to cancel your membership, you will always have access to courses and bundles purchased prior to becoming a member. However, you will lose access to membership-only series (e.g. Hands On Labs, Community Insider, Release Review) and any course you've started that were not purchased prior to your membership.