I think a fair solution to this would be for Air NZ to offer to cancel Koru Memberships on request and refund on a pro-rated basis similar to how insurance companies do it for car insurance.
One thing to note is the Koru Lounges still haven't closed - them closing would certainly make for a better case for refunds.
On a personal note, I'm sick of being lynched by some members of the forum everytime the commercial policies of Air NZ are questioned - they might have a $900M hole, but I'd rather take that than explain my now worthless $700 membership to the significant other, it's not pocket change for a lot of us.