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.
Discussion
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/#/
