Cloned node entity reference field stay in sync with parent node
1) You could use a hidden field of the same type with the same information. This way, the information relating the parent to child can be reverted, regardless of the changes or overrides. Use Rules to populate the duplicate field. Create a "Revert" button on the node and again use Rules, or as a form submit to react to copy the information from the hidden field to the visible one.

2) Use Rules to adjust any child nodes when the parent is saved/updated. This would act on both the hidden and visible field, with a condition on the visible (not to change if it has been overridden).

You could also write a module to do this, but I think it can be done with just Rules.