The last Bitcoin is projected to be mined around the year 2140, based on the current rate of block creation and the predetermined supply limit of 21 million coins programmed into the Bitcoin protocol. The Bitcoin network's reward for miners is comprised of two components: the block reward and transaction fees.

Block Reward: Currently, miners are rewarded with newly minted bitcoins for successfully adding a new block to the blockchain. This reward is known as the block subsidy. However, the block reward undergoes a process known as the "halving" approximately every four years. The reward is halved, reducing the rate at which new bitcoins are created. The halving events continue until the maximum supply of 21 million bitcoins is reached.
Transaction Fees: In addition to the block reward, miners also earn transaction fees for processing and validating transactions included in the blocks they mine. Transaction fees become increasingly important as the block reward diminishes over time.

After the last Bitcoin is mined, miners will rely solely on transaction fees as their source of revenue. If the demand for Bitcoin transactions remains high, it is expected that miners will continue to be incentivized by the fees paid by users for transaction processing. The hope is that the transaction fees will be sufficient to maintain the security and functionality of the network.

It's important to note that the dynamics of the Bitcoin ecosystem can change, and the network's sustainability will depend on factors such as the adoption of Bitcoin, transaction volume, and user demand. Additionally, technological advancements, changes in consensus mechanisms, or alterations to the Bitcoin protocol could also play a role in the long-term viability of the network. The Bitcoin community and developers will likely address these challenges as they arise, adapting to ensure the network's continued operation.