What about the problem that a network with very small hashpower becomes an easy target for government attacks?
Discussion
Why should hashrate ever decrease, though? ASIC can be liquidated cheaper and cheaper until it's profitable to plug them again.
On the short term (2 weeks). The difficulty adjustment will increase and the attacker should employ more capital and more power until it reach its objective or the attack becomes prohibiting costly.
No concern about that scenario.
The 51 % attack is also related how colluded the mining entities are; here again, is the decentralization of mining entities which brings solution to the situation.
By the way, these numbers give me evidence, there is participation in mining operation which could survive the coming halving. So no rush on this fee and mining topic addressed by @fiatfaj
web.public-pool.io/#/
If the total miner reward per block is $10 how much hashpower do you think you will get?