I don't think bitcoin is a bubble. It is a great technology that can help us to improve a lot of things in the modern society. However, as a bitcoin investor my biggest fear is that bitcoin could gradually be displaced by other cryptocurrencies making its price decrease until practically $0, because the crypto market has shown to be so unpredictable and subject to speculation that from one moment to another something could go wrong and ruin a lot of investors.
I am aware that even at $1.00 bitcoin would continue to be an efficient means of payment, but such a low price would discourage miners and investors from continuing to support the cryptocurrency.
If you saw Bitcoin heading towards $0 I am sure you would switch ships for the rising currency (er I hope). I don't think we will ever see that scenario though, the lowest pundits think Bitcoin could fall is around $1200-1300 mark. I believe that is around the cost to produce a Bitcoin although I could have that aspect incorrect.