What happens in 2140 when the last BTC was mined with the confirmations of the transactions in the blocks and thus with the block rewards. There should not be more BTC than Rewards, because 21 Mill BTC were gemined.
How are the transactions then confirmed?
In theory transaction fees will "reward" the miners, but unless computers become smaller, faster, and smarter, then I doubt there will be any profit in this. One solution to this is to move over to a proof of stake system, but then again, how will this really effect Bitcoin prices? 2140 is a long time away... Its hard to say how many advancements there will be. Perhaps there will be a whole new system altogether.