I think the bitcoin will fall because of RANSOMWARE,it is impossible/Difficult to track who did this and in futur Bitcoins will be considered as a motivation mean for such act
I do not want to say that you are wrong, i mean it could happen that this will be start of more and more ciber attacks. But i do not think that it is untracable. There is always a way, and not to speak that if it becomes a problem in the future, it would be dealth one way or another. Bitcoin has made a long way to this point, and it will be hard to die after so long.