[jltsiren]

The accepted response is escalating the situation on the diplomatical level. Imposing sanctions if necessary. Getting other countries impose them as well. And, in extreme cases, trying to get the UN Security Council authorize military action.

[pseg134]

Well they killed him and haven’t had any real consequences so I would say killing him was also an accepted response. It was accepted by everyone realistically able to do anything about the situation.

[jltsiren]

Not facing real immediate consequences is not the same as acceptance. Especially when we are talking about acceptance in the moral/normative sense.

Besides, you should wait at least a decade or two before talking about consequences. Things don't change that quickly in international relations, because the stakes are so big. But they do change, as you can see from the relations between Russia and the West.