Bitcoin is going no where , something that is primarily never go out of fashion as in future we will see good altcoin which is better than btc in every aspect but still btc will not go out. As for Blockchain it is revolutionary technology and it will keep on improving in future so its growth is endless.
That's what is really important. Bitcoin isn't a stagnant entity, it keeps improving all the time, because a great team of developers is behind it. How can we say that something is "might be over" when it hasn't reached its full potential yet? And I agree on the fashion part. Only I think there is a reason for that, which is much stronger than simply BTC to be a "fashion thing". It can appear to us that there is a "good altcoin which is better than btc in every aspect", but it is very likely that time will prove we were wrong.