Did you bother to read your Air Law & Op. Procs books? Or was it simply a 'learn/dump' process, in your case?
You can either revalidate your Class Rating by experience or by proficiency check with an Examiner. If you elect to fly a proficiency check within the final 3 months of your Class Rating validity period, your Class Rating will be revalidated for 2 years from the date of expiry - otherwise it will be 2 years from the date of the proficiency check.
If you let your Rating (not licence) expire, you will need to renew your Class Rating by flying a proficiency check with an Examiner.
The proficiency check is simpler than than the PPL Skill Test, but it will include a navigation element.