As I wrote before, my "ideal" scenario would be a sidechain-backed tail emission plus fees.
I agree with this I think tail emissions plus fees are the best option long term. Transactions fees would need to be much higher to sustain current levels of mining hashrate which would scare people away from using the network. But also I fear the variability of transaction fees would destabilize the network. Tadge Dryja makes some good points about this in this MIT lecture
https://www.youtube.com/watch?v=wXWbdiOBW5w at 58 minutes in. During large fee periods miners could end up fighting to reorg high fee blocks instead of mining new blocks.
Of course if hashrate dropped now to 50 EH/s, 95% of all miners went bankrupt and sold their equipment potentially to attackers, then the network would be seriously in danger.
One possibility is if mining fees are low enough to be vulnerable to attack large bitcoin holders could have mining power on stand by to turn on in case of an attack but that might just be wishful thinking. If I was Michael Saylor id probably have some rigs on stand by.