So when the rewards drops to zero the average fee could be $7.6 * (5+1) = $45.6
So at about 1MB blocks and 0 block reward we have a $45.6 minimum to support the current network at current levels.
You are looking at it entirely the wrong way. When the network is no longer supported by the block reward and instead by transactions, it doesn't mean that the transaction fees have to rise.So at about 1MB blocks and 0 block reward we have a $45.6 minimum to support the current network at current levels.
There's nothing particularly wrong with a decrease in the amount of money flowing to miners. Gradually, the miners' rewards in BTC will most likely decrease. If the fiat value of their rewards also decrease, all it means is that mining will be less profitable, so a lot of miners will pull out.
The system regulates itself in this regard. When the rewards decrease, so does the computing power dedicated to the network.
It still wouldn't be particularly concerning security-wise, because an attacker would still have to pay billions to orchestrate a 51% attack.
