They don't realize anything and they don't care, all the leadership in these companies have no vision beyond goosing the next quarter's numbers. They have been promoted to the top because of their ability to meet targets, nothing else. If they see weakness in Europe they will compensate by pushing more ads, lay off some people or increase prices to keep the number go up.

They are all sitting ducks for black swan events, but I don't think getting roasted in Europe will be enough to trouble them.