I don't think "cut off completely" is necessarily a figure of speech. 3 of my friends are CO, and while 2 of them still try to contact their EAC, they receive no contact in return.
Granted, estranged family members often run into each other on the street (if they live near each other) or at larger family events. So in that sense, I can see where CO or NC may be figurative. However, these encounters are often very awkward and painful, to my knowledge, and don't always involve any communication.
Also, I know people sometimes have a change of heart and resume contact, especially when an estranged family member is ill/dying, as you did rose. But IDK if they always realize they will do that when they first go NC. And I've read posts on MN where they said they would "never" reconcile, even if their mum/MIL/etc. were at death's door. Sad but sometimes true.
All that being said, these are some of the reasons, I would go LC rather than NC if I my relationship w/ a parent or other family member went sour (except in extreme cases, of course). But that's just me.