A general point about "intervening" when the person who is geting hurt doesn't want it. (This isn't directed particularly at thec situation we've ben taklking about.)

The only things that matter about intervening is that it should helps. There are some situations where there just isn't any way of intervening that isn't more likely to make things worse - increase isolation, precipitate a tragedy etc etc.

In which case, you just have to stand back, and be ready to help when help is possible. And awful things can happen in the meantime.

Maybe it might make people feel better to have intervened. "I did everything I could." But making yourself feel better about it isn't the point.