A domain registration can’t be revoked and the domain will expire on the natural expiration date if the renewal is not requested (only if the domain has the Auto-renew OFF).
Domains registered through Rebrandly become part of their system and expire according to their original registration period (after 1 year). They cannot be deleted or removed from your dashboard until they will expire and only after the grace period and the redemption period (usually 70 days after the expiration date). If not renewed, they will be automatically removed from your dashboard. In the meantime you have to add another domain slot if you have used the available ones.