I think it depends on the nature and size of the attack(s). If they were quite large (hundreds of people each) and in multiple countries, perhaps even coincidental or at least very close together I think Europe's attitude would shift dramatically towards encouraging and taking part in retaliatory action. Moreover, don't forget that despite the official PC-ism of Euro governments there is a great deal of prejudice in these formally monolithic countries. Remember...Europe wasn't built by immigrants the way The U.S. and Canada were. Many of my friends on the continent, and some are quite left wing, have expressed a great deal of animosity towards the moslem immigrants, many of them illegal. Were a critical level of violence to occur, I think we could see a Europe far different than we do today. The trick will be keeping it from decending into one of its darker behavior modes.
Please do elaborate?