So it is year 2024 and the max BTC supply is reached at ~21M.
I'll speculate that the price of energy around the world will be higher than it is today, so that will cut into the miners profits. They will also be receiving their BTC on fees alone, not the generation of BTC for completing the block (like today).
Will it be economical to continue mining BTC going forward? The large mining operations can always set up a solar panel system to reduce energy costs.
Even if some of the larger miners shut down, I'm sure there will be enough miners around the world where the blocks will still be completed, but it may take longer. (The mempool may grow like it did before X-mas last year) I'm not exactly sure how the lightning network will affect the mempool....?
Is it possible that the S/W for BTC may be augmented to a semi POS type of system?
Last supply of bitcoin would be mined is on year 2140. I dont know where you do get that year 2024 but it isnt the right year. Miners would be still on work even though they are not mining but yet they would still earn profits on making confirmations or pushing up transactions among the network and i do believe on those years fees would really be high for sure.The question is if bitcoin would able to survive into those years.