Bright, I do believe there are degrees of MLC. If they do a lot of damage it is harder for them to return - assuming they want to. It really is a question of letting go, and being as pleasant as possible while setting boundaries.
Someone once said it is a fine line between being a b*tch and a doormat.
I think we get to the point when we ask ourselves, would I want this person back in my life? The power is with us - when we are abandoned it feels as if that person takes the power away with them, and gradually as we work on ourselves we start to believe in ourselves again.
For a long time we see ourselves through the eyes of the abandoner, as worthless, but they are wrong, not us. We are people of worth, and they are the ones with problems. Actually internalising this takes a lot of time and work, Easy to say, much harder to do.