[creato]

How quickly would the difficulty adjust? My understanding is that there is an algorithm that slowly adjusts difficulty. If a big chunk of the ASIC miners went offline and mining reverted to individual GPUs, it might be a very long time before the difficulty reverted to something reasonable.

[tromp]

Bitcoin difficulty adjusts every 2016 blocks, nominally 2 weeks. Each time it can adjust by a factor of at most 4 (in either direction). Many other cryptocurrencies adjust difficulty every single block.