To be brutal, we can always make excuses to stay. Oddly, while most women are in dire straits the first 12 months of a separation, they are usually better off from that point forward. It may be hard financially, but is it worth sticking around for a child to learn that being abusive or being a drunk are acceptable ways of behaving? How do you measure that cost?
I had a friend who left her wealthy husband and ended up in a homeless shelter with three children for the first two months after she ran away. She is now a successful business woman in her own right (with some help from government grants). She waited too long. Her son learned that as long as he paid the bills he had the right to be verbally and physically abusive to any woman. Her eldest daughter pretty much takes whatever her husband dishes out. Her youngest daughter stands up for herself. She lets no one bully her. She was 4 when my friend left her husband. The other two were 12 and 14.
Sorry, this is my own personal soapbox. I used to work at a woman's shelter. It takes courage to leave. It takes courage to not return. The rewards of leaving, however, far outweigh the benefits of staying, no matter how difficult it would be financially at first.