The answer to your question is the answer to my question, and I actually have no stake or opinion on whether these lands should be returned. Maybe they should. But who should get these lands if we follow criteria resembling the laws of modern civilization (which is the one we'd have to apply here)?
That's the problem with collective ownership - nobody and everybody "owns" the land, and you can say they still own it the same if they still live in New Zealand. And, based on my very limited understanding of their history, they themselves couldn't ensure any sort of ownership given that land changed hands based on frequent warfare and conquest initiated by their chieftains.
About the Rockefeller foundation... You can check the laws that govern the continuation of his property, they are laws that apply to everybody and are codified in books of law.
> there is no guarantee that current descendants would be the ones actually owning the lands today.
Say what now?
Much the same time as John D. Rockefeller was born the Treaty of Waitangi was "signed" in 1840 (there's some conflict over versions and translations and genuine evidence some people signed an English language version after being shown another version in their own language etc.) and birth records and family histories from then until now are pretty solid.
Again, why should anyone respect the legal agreements about the Rockefeller trust if no one can be bothered to respect the agreements made in the Treaty of Waitangi?