This morning I was talking about this with a buddy of mine.
Right now we have miners all over the world trying to solve this exponentially hard algorithm to earn their bitcoins. That is their incentive and that is what drives them to do so.
What happens when we remove that incentive to "mine" aka "verify transactions" on the blockchain? What I'm basically asking is what happens when we hit 21,000,000 bitcoins from the perspective of the miners?
Well, there are only two scenario when that happens. First, btc miners will stop working. Second, these btc miners might shift to different (and probably newly introduced) cryptocurrencies . But again, I think this will not be coming sooner for the algo of btc is not that easy to solve and 21m is a lot of btc, if you get my point, tho. However, miners CAN still stay on working with bitcoins BUT only earn from transaction fees.