I'm starting to come to the view that pre emptive shunning of them is the right course of action. If the threat of shunning or conditional friendship is invoked by them then just lay the cards down on the table and tell them what happens next if that is the way they want to proceed, rather than be the victim of shunning, own it and use it to your own empowerment and self preservation.
No second chances unless it is heartfelt and honest. Any "terms or conditions" imposed results in them staying in the "no fucks given" column.