When a datum plane lose his geometry reference, Creo doesn't highligth the problem. Creo just keep the datum plane as a "dead geometry".
Nota : I use Creo 7.0.2
For me it is an important problem because, often, when I make modification in my 3D model I remove some geometry. Recently, I discovered in a prototype that a clip didn't have the good localisation because the plane who pilots his localisation isn't up to date because of this problem.
For example, in the case of the image above, you can see that the datum plane "debut_guidage" (I'm french) seems to be normal but when you open the editor of this function, you can see that the reference is consummed. It is real, the reference is consummed by the function "Enlevement 4" but as you can see Creo doesn't warn us about the problem.
I called the PTC assistance, they didn't find a way to answer to this problematic and they suggested me to make a proposition here.
Nota : I observe that the function Round also doesn't highligh consumed references.