now what ?? then its complete mature no one can mine bitcoin anymore you can only buy them from someone who hold them and your question "does BTC just end?" doesnt make any sense bitcoin can still operate even with one computer cpu mine it the difficulty will change every 5 block (CMIIW)

This is too far into the future to know what will happen. I see miners continuing to secure the network to collect transaction fees and a sky-high price to justify their efforts. There is also a possibility of a fork to modify the incentive structure.

There were many threads earlier regarding this topic, first it will take a long time for all the coins to get mined and second important factor is that the price would be so high and we need a better solution to counter the price when it comes to transaction charges, bigger blocks was one solution but the question remains how big the blocks can be and whether we can have a better solution than we have now to balance everything. Even now the miners will be earning a few extra bitcoins apart from 12.5 bitcoin they earn with every block and by that time the price will be that high that they will compensation with the transaction fees alone.

1 bitcoin per year how your calculating its based on the blocks are mined it should be blocks are mined . there is around  12.5 bitcoin per block . Per day it will be more than 100 blocks are mined .

Even after all Bitcoin yet to be mined gets mined, that doesn't stop transaction confirmation or won't transactions be mined as well and confirmed on the blockchain? To me I think provided transactions are still being made with Bitcoin, there's no such thing as Bitcoin dying. What we will fear is transaction cost being high once again to enable miners cover cost for their equipment and time.

Once quantum computers begin appearing and if one quantum computer can brute force the private key by feeding it only the public key, that will be the end of cryptocurrencies as we know it.

There are also quantum resistant ledgers, I wonder how these blockchains will fare vs a quantum computer.

This shows the end of Btc won't happen with the mining of last Btc. As the price gradually keeps increasing, so will it be when the last coin gets mined the price won't be the same again.