She knows he may do harmful, disruptive or damaging things like reporting her to child welfare, call her workplace to  annoy her or interfere with her employment, file unfounded and unnecessary lawsuits, etc. He has promised her he would do such things or has actually done some of them in the past.  All of these are tactics to keep her under his control, and it is he who is creating this problem.  Rather than her leaving, shouldn't he be stopping the abuse?