What will happen if people just stop buying bitcoin? Will bitcoin be as usable as now Or will it be a step towards the end?
How will the market value react to it, people wanting to sell bitcoin but there is no one to buy.
I think that there's a the possibility of the world's random reactions to make all these "what ifs " happen is just impossible .
But supposing it could happen ,when the normal outcome won't be any different than any other market when it looses it's customers/investors , the supply and demand low will be applied and the more bitcoins will be mined the more the total value per coin will decrease .
However, if it does, if the demand lowers its price will lower until it is worth 0$.
The price of the currency would simply be zero. If there is no offer, there is no demand, and vice versa.
The maths should give something like this :
(taking the actual total market cap of $224 073 314 000 USD and dividing it by 21 Million coins which is the max total supply )
= 1 coin will be worth $10670 .
So even if the OP's "very unlikely if not impossible to happen" actually happens , and that no one buys or withdraw it , and when all the 21M coins will be mined , the value per coin will not be 0 .