What I will do is leave my life. There was a life before bitcoin, and people were actually doing great even before the development of the currency. Since there is always a saying that nothing lasts for ever (even though this won't happen any way or anytime soon in the next 100 years to come), we will just have to continue our lives where we stop, and the thing will affect many people, increasing the poverty rate. There will definitely be chaos, but people will move on.
So if this happens, one will have to start looking at other businesses that I have as a primary source of income and not secondary ones again. To be honest, I really don't know what I will do until then because I always have that positive mindset towards bitcoin, and it still remains. Just as a country's local currency can't go back to zero again, that's how I believe bitcoin's value can't be reduced to zero again, at least not in this generation.