What if transaction fees aren't enough to incentivize the miners to secure the bitcoin network? I think this is a potential problem we may see in the next few decades as the halving continues on. My hope is that we will have enough people using the bitcoin network to have a healthy fee market, but if we have weak periods like now where there are several unfilled blocks, wont miners just turn off their equipment as they are unprofitable? What options or solutions are being discussed to help mitigate this?
The difficulty adjustment is designed so that mining is always profitable for the most efficient miners, regardless of the value of the block reward.
The real question is whether or not the block reward is high enough to make a 51% attack economically infeasible. One consideration is that if it is not, then perhaps it is because Bitcoin has failed and is not worth saving anyway.