> ...mining just stop producing new coins but continue being profitable with just the transaction fees?
The profitability of mining never really changes. When rewards for mining increase, profitability briefly increases, but then more miners join, the hash rate goes up, increasing the cost of mining and bringing mining profits back to equilibrium. And vice versa: if rewards for mining were to go down (for example as the block reward reduces according to schedule), the least profitable miners leave, the hash rate goes down, decreasing mining costs and bringing mining profits back to equilibrium.
The hash rate follows total mining rewards (the sum of block rewards and transaction fees). Mining costs follow the hash rate. Mining profitability is the difference between mining costs and mining rewards.
The profitability of mining never really changes. When rewards for mining increase, profitability briefly increases, but then more miners join, the hash rate goes up, increasing the cost of mining and bringing mining profits back to equilibrium. And vice versa: if rewards for mining were to go down (for example as the block reward reduces according to schedule), the least profitable miners leave, the hash rate goes down, decreasing mining costs and bringing mining profits back to equilibrium.
The hash rate follows total mining rewards (the sum of block rewards and transaction fees). Mining costs follow the hash rate. Mining profitability is the difference between mining costs and mining rewards.