Separating surface land from mineral interests

I work for a not-for-profit foundation and have been of the belief that if land is gifted to our foundation the smart thing to do is to legally split the mineral interest from the surface land before selling the land.

Is there ever a reason to not split out the mineral interests? If you split the mineral interest from the surface land are you always guaranteed access rights to harvest the minerals?

In North Dakota, you will have to claim the severed mineral rights every 20 years in order to continue to "own" them. Otherwise they will revert back to the surface owner. They have an easy form to fill out. I think if there is production, you don't have to do it.