If all 21 million bitcoin's be mined, the miners will remain on the reward of transaction fee. The price of Bitcoin will go very high and the miners will solely depend on every transaction made.
What if a hard-fork is made, will it extend the total supply of Bitcoin in somewhat manner or it has nothing really to do with the Bitcoin blockchain, cause this is being the next thing that is being expected or which has been done like the BCH which was one done because of the rapid increase in the price of Bitcoin.
Well, I don't really know the technicalities of the hard-fork on Bitcoin, but I do know that Bitcoin will be very expensive as the holders will keep hold on it, and demand will increase, so will the transaction fee increase alongside.
The price of bitcoin will continue to rise even though mining is still active, if 21 million has been used up in mining then the price will skyrocket and get out of control, this is a passion for us to continue to hold bitcoin and make it a long-term investment because with 1 btc we store in cold wallet then we have the opportunity to become rich people.