Existing use rights under section 10 do not apply to:
- reconstruction, alteration of, or extension to, any building that increases the degree to which the building fails to comply with any rule in a plan or proposed plan
http://www.qualityplanning.org.nz/index.php/manual/enforcing-plans-and-consents/existing-use-rights
Existing Use Rights are based on coordinates. When a landslide has occurred the coordinates are not correct and EUR are no longer valid. If a property falls off a cliff EUR do not travel with the foundations of the house. They are voided.
You can insist on EUR certificate to prove that these rights still exist. Assuming EUR when they are not confirmed may put you in an undesirable legal position.
Another point that I have debated with CCC planners is
If your floor levels will be lower than when the property was legally established that would increase the degree which the building fails to comply with any rule in a plan.