We often invite men to connect to the issue of violence against women by saying, "What if were your mother? Your daughter? Your sister?" While this invitation is understandable and respectable, it's actually the wrong question to ask.
If we agree that someone should have helped Nigella, then we've got to hold ourselves to the same standard the rest of the time -- to respond to, reduce and prevent the everyday acts of sexism and discrimination that add up to or excuse violence.