Justified? That's not relevant. The father after witnessing his two young sons being killed by a reckless individual understandably snapped. How many of us can state conclusively that in the same situation we wouldn't react as irrationally?
It’s doubtful I’ll see any news on how this concludes, but I’m still thinking jail time. Also, I would not be surprised in the least if the dead drunk’s family lawyers up and comes after the guy.