Well, of course the European Union doesn't have very many other choices, aside from putting sanctions up as its first response.
Now, NATO could do one of several things. There are a lot of risks in the sense that already NATO has deployed troops forward, close to the border, and of course there's a risk that if Russia gets into Ukraine, it might start to get greedy, and that greediness could obviously go to places like Georgia, where it also has other instabilities, or Kazakhstan. That would be another risk.
One issue is that they have prospectively concentrated a lot of their military forces in the west, and, in the way that they used Sochi to move down into Crimea after the Olympics, as a springboard, they might decide to pivot and go somewhere else. Their goal, more or less, is to keep the irritation high and to keep NATO in a situation where it prefers not to respond with violence because it doesn't want to look like it's escalating. This gives Russia a large amount of room to manoeuvre, particularly because it can use civilians. It doesn't necessarily need to have soldiers who are identified as soldiers doing the activities. That's something, of course, that NATO and other states are not doing, because they have to wear the identification, so that's another thing that benefits Russia.