A fad, by definition, is a short-lived craze. Bitcoin has been around since 2009, which means it's coming close to the 10-year mark and that, in my opinion, hardly constitutes a fad.
Yes, that is what I was thinking also...almost 10 years and still growing in popularity/value is getting a bit long for bitcoin to be written off as a simple fad. In other words I think we are past the "pet rock" stage here and well into something that is a real phenomenon worthy of consideration. Bitcoin may not completely replace fiat currencies but over the long term it can still remain as a quick and convenient way of sending money, particularly across international borders or in situations where transacting in "normal" currencies has become difficult.