Let's say "let's cross the bridge when we get there". Very difficult to see what will happen, maybe the price will go to $1 million or go to 0. We even have difficulty predicting what's going to happen in the next year or so, what's more 10-20 years from now?
Yes it is a long way to go, we do not even know if we can see the time when all bitcoin are mined. We also do not know whether all bitcoin can be mined or not as there might be a chance that bitcoin is not even being used anymore before all are mined. Anything may happen in technology, who knows the future? No one obviously.
Yes it will be on 2140 by that time and I will be dead when that year comes, so I must say it would not be my problem anymore if all bitcoins will be mined. But just to explain it you further what will gonna happen. This explains it.
"Originally, 50 bitcoins were earned as a reward for mining a block. Then it dropped 25 bitcoins, and then to 12.5 bitcoins. In 2020, it'll drop to 6.25 bitcoins. So if we do the math, if there is a having event every four years, the last Bitcoin should be mined sometime in the year 2140."
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hereto clear your mind.