Entertainment and dramatic endings could have been achieved without Helen ending up being the one in the wrong. I have listened again, and it defiantly sounds like she stabbed him, paused and said sorry and then continued to stab him over and over once he was no long a threat. She passed the point of self defence. Manslaughter on the grounds of deminished responsibility.
Helen works up to leaving slowly, having gained control over all the money and turned over the PR on Henry, once safe she confronts him, he gets violent, but someone leaps in and saves the day. All his past misdimeners are revealed to the whole village, he is publicly shown up and humiliated and leaves. Which also gives the possibility of him returning the the future etc etc.
And another plot hole- he didn't come back early, he came back late. He apologised for being late.
And it was a tuna bake apparently. Not pasta or a pie!
Oh, and when Henry came back down, we don't know who was holding the knife, but he'd be no help as a witness. He came down, Daddy shouted at him to go upstairs and then Mummy stabbed Daddy repeatedly.