There is the critical ArM5 p.112 Durations Momentary: "Ritual Creo spells with Momentary duration create things that last as any other thing of that type. The magic is gone in a moment and so cannot be dispelled. This also applies to ritual healing spells."
Tmk there is no such statement for D: Momentary Formulaic or Spontaneous spells - and without such a statement, objects created by D: Momentary Formulaic or Spontaneous Creo spells will just disappear after the Duration expires.
To verify this, you can also look up HP p.116 Create a Human Corpse: "This ritual creates a human corpse. The lowest level ritual spell can be is 20." If after many years of ArM5 development there were a level 10 CrCo Formulaic spell creating the same natural human corpse, it should be in this place.