Estrangement, IMO, is a very painful thing. Then again, if a relationship is painful, in itself, I imagine estrangement can be very freeing for one or more parties to the conflict.
I agree with PPs (previous posters) that it shouldn't be done lightly. Efforts should be made to talk things through. Since mismatched expectations are often involved, I think those need to be explored, some people don't realize that the other person had a different vision of a situation than they did. Boundaries may need to be set, in some cases, and others may need to find a way to accept them. If one person tends to make offensive comments, etc. the other may have to call them out on it and let them know how they feel about it. Apologies may need to be made and forgiveness given, if possible.
Hopefully, the people in conflict can come to a point of understanding. If not, in some cases, contact may need to be cut back to decrease chances of friction. Only when efforts to fix the relationship have been tried - and failed - do I think estrangement is in order.
I get HettyMaud's feeling that a CO should occur only in the event of a "criminal act," such as abuse. However, would say that should be the only reason for an IMMEDIATE CO. At the same time, I can see a CO happening if non-criminal, non-abusive offenses are committed over and over, despite requests for them to stop. Also, as has been mentioned elsewhere, I think there is such a thing as "death by a thousand paper cuts." A steady stream of nasty acts and comments, no matter how "minor, can, no doubt, drive some people to estrangement.