Just bear in mind three things, my friend:

1) CPS calls can be anonymous and you don't have to tell anyone you made the call. I'm sure many others are aware of the incident, and neighbors, friends, and other family can all share everyone's suspicion.

2) Mandated reporters (i.e. teachers, healthcare workers, police, etc.) are required to call if they have a suspicion of 5% probability of abuse or greater--this means that even if most of their whole soul doubts the abuse, but even a slight part does, they are legally obligated to call, and CPS will sort it out from there. The police should have called, but may or may not have. Additional calls are documented, and even if there is not enough evidence beyond lots of calls, simply having so many calls can spur action from CPS.

3) This sort of thing affects children more than most people realize, and letting things play out might result in a worse outcome than expected. Women in abusive relationships tend to be incredibly forgiving, and this "last straw" may merely lead to another honeymoon period and further abuse of the wife and potentially the children.

Do what you feel is right of course, but I'm just suggesting you shouldn't let your fear of reprisal interfere with what is in this woman's and the children's best interests.