I don't know... Itachi never seemed the type to lose it that way. I think the only thing that would happen is, the killer would regret it and the village would be in trouble if they were the reason behind it.
I'm not sure. Itachi has a lot of self control but then again the Uchiha anatomy causes them to go mad and lose control. He would probably gain a new power from his hatred (Perfect Susano'o etc.) and go kill Danzo, Obito or whoever is responsible for this act - Itachi fighting Haku: that would be quite interesting.