prevent objects from being deleted

Hi

I wanted to do something rather simpel.
I've made an important Rig here that is used many times in many scenes now. Sometimes there is an error in the rig though and I found out, that often this came from parts of the rig that have been deleted by the artist. so I want all the parts of the rig to be undeletable.

So I tried the #NodePreDelete callback. In the function I check if parts that are about to be deleted are part of the rig. Untill this point its working and it's indeed rather simple. but the question is, how can I prevent the objects do be deleted. I tried to get rid of the unwanted rig-parts in the selection, but that made 3dsmax freeze and max internal scripts created a lot of errors then.

does anyone have any Ideas? or completely new ways to try?

PS: I tried to create copies of the not to delete objects, but as they are part of a big rig, the rig stopped working after this. The Objects simply can not be deleted.