IMO the fact she stabbed him causes complications. IN casualty some years ago one of the characters was in an abusive relationship - proper violence, and she pushed him down the stairs one night as he tried to go for her. He spent some weeks in hospital and then died iirc but she wasn't charged because it was self defence.
There's no way this could be upheld as self defence - ever. In fact it would be unrealistic to even think that she wouldnt' go to prison for this.
What they should have done is have Henry run up the stairs to get away from rob, have rob go after him and when Helen tried to stop him he try to grab her and her pushing him off balance down the stairs... ... Deaded. and the abuse would be seen as mitigation.
It's a bit of a dangerous road to go down to suggest that emotional abuse could be seen as mitigation for stabbing someone multiple times.
I think that Rob will die. Helen will go to jail, Tom and Kirsty will get back together and will raise Henry and the baby. And Helen will just disappear when the new editor comes on the scene.