With the conclusion of Bitcoin mining in 2140, miners will rely solely on transaction fees to sustain their operations ?
Currently, miners get the block rewards and the transaction fees. The block reward is halved every 210,000 blocks and will decrease to zero when we reach the block number 6,930,000. In that time, there will be no block reward and miners will only get the tranaction fees.
It may worth mentioning that the block reward decreasing to zero in 2140 is only an estimation. It may be sooner or later.