This topic came up at an instructor conferece last year.
The delegate from CAA said that if for example, the holder of an ATPL was to not use their NZ licence for 5 years they would need to re-sit a law exam upon wanting to return to recreational flying. Regardless of the fact that they only want to exercise privileges of a PPL they must sit the exam for the lifetime licence they hold. In this case, an ATPL law paper.