How to get a free .arpa domain

Many people, including myself, tend to look at .arpa and think "oh yes, thats PTR queries" but forget the DNS doesn't have a global rule that ONLY the PTR query can be sent to the domain.

It's just a domain. You can put anything into your zone. A, AAAA, PTR, TXT, you can even put HESIOD records if you want to party like its Kerberos nineteen ninety IV.

Do these free HE assigned IPv6 prefix(es) just remain valid indefinitely even when not actually being used/routed?