Them having Raina killed instead of Tariq is actually good writing imo. It would have been way too eazy to have Tariq's dumb decisions bite him directly. We all would have seen that coming. Most of us have become extremely annoyed with him, and would have had no problem seeing him killed at this point either. Having him murked would have literally just been them giving the audience what they want. Having Raina killed instead of Tariq gives that part of the plot a slight twist that most of us probably weren't expecting.
Now we get to see the emotional effect that being directly responsible for his sister's death has on him, and the actions that will come from those emotions.