You break contact with an ex for your own mental well-being, and to quickly move past the emotional chaos. She should be dead to you.
"No Contact" is not some kind of method to get her to come back, because even if she does, the reason for the break-up in the first place hasn't changed... the only thing that might have changed is her 'willingness' to settle for you. Which if you take her back, will only cause in her resentment, which she will blame on you.
You can never go back because there is too much baggage. It's better to have a fresh start with a new girl... not so much baggage to carry.