People don't think 150 Years ahead of time while inventing anything. What will happen in 2140 is beyond our scope. There could be no bitcoin at that time and mankind may have shift to some other form of currency. Also the world would have ended by that time. I think its useless to think of the time when no one of us will be alive to see that day.
My thoughts also. By that period, all human beings that are living today are already long gone. We don't know what is status of the humanity at that stage or the condition of our planet. Just think of the climate change or the global warming attached to it. After more than 100 years, no one can tell what our future will be. Maybe, bitcoin will already be an obsolete technology and there is no more reason to think about it. So right now, it is not really good idea to think about that period of humanity, if ever humanity still exists.