The hope is that miners will still make money off of transaction fees (a "tip" to the miner which verifies the transaction). Each new block assigns 50 BTC to th

The hope is that miners will still make money off of transaction fees (a "tip" to the miner which verifies the transaction). Each new block assigns 50 BTC to the miner that found it, plus the accumulated fees of all transactions included in that block. The idea is that as mining new bitcoins becomes unprofitable, the transaction fees (set by the initiator of the transaction) will make up the difference. That theory has yet to be tested, though.