The root servers do not deal with registries. They deal with the Root Zone Manager (Verisign, under contract to ICANN) only.
The way you "destroy" a name is either to not delegate it or give it to the Registrar of Last Resort (https://www.rolr.eu).
The way you "destroy" a name is either to not delegate it or give it to the Registrar of Last Resort (https://www.rolr.eu).
In theory the law makers could specify this in law as form of registry regulation, but no one want to do that just to address one or two court cases where this question comes up. The registrar of last resort doesn't give any direct answer to those questions either.
In general, the vast majority of registries are fine with marking particular domains as "allocated but not delegated" as long as they get paid. ISTR ICANN waiving their fees, so the costs of marking a domain as undelegatable essentially turn in lost opportunity cost, which most registries are willing to eat.