After passing the Foundation exam, your Foundation Certification will be valid forever.
After passing the Practitioner exam, you're eligible to become a PRINCE2 Registered Practitioner.
If you don't apply for Registered Practitioner status, you'll still be PRINCE2 qualified and can use 'PRINCE2 Practitioner' (rather than 'PRINCE2 Registered Practitioner') on your CV, business cards, and elsewhere.