No one can predict what exactly will happen in the future. In the event of a nuclear war, they can turn off electricity and the Internet, no currency will have value.
Who know by that time internet developer had discovered some means of connecting people other than internet, and or Internet is transmitted thru signal directly from the satelites(and mobiles and computers are capable of receiving this signal) that is far from being destroyed when world war started . And electricity won't be a problem because probably by that time, solar powered cell are well developed and widely used by every person on earth. I am just riding on what you are saying about the unpredictable future .
My personal theory is that cryptocurrency is not the bubble, but rather the needle that will burst the fiat money bubble. Trough history we have always had an easy way to attribute value to things without it. Those who believe that fiat money is the only true way often attribute their opinion to the fact that fiat money is substainsable because of its centralized nature and its history of being used as a represantation of value
Right now it is (for the most part, at least)
Bitcoin and other cryptocurrencies fit well into the definition of a financial bubble. I could even claim that Bitcoin is a sort of tulipomania. Just like tulips, bitcoins are useful for some purpose, namely, for transferring value around the world while completely bypassing centralized (real controlled) entities like banks, but Bitcoin current price is by no means determined by this utility. Most of Bitcoin value today comes from sheer speculation. Whether Bitcoin bubble is going to pop eventually or its real use as a currency will finally match its use as a speculative vehicle is not clear as of yet
I do agree that cryptocurrency are still in a stage of a financial bubble until the market is saturated where the true value of cryptocurrency is visible.