Now, the price of Bitcoin will certainly drop to the level below 2 pizzas for 10,000 BTC, but I'm sure some people will be still mining almost empty blocks on their laptops, just in case. They will be able to do that on their laptops because the difficulty will drop to the appropriate level.
that assumes the network will reach the next difficulty adjustment. let's say the event occurs shortly after the last retarget. if the only machines left mining are laptops, the hash rate may drop so drastically that the network will never reach the next difficulty adjustment. the network could literally grind to a halt.
Great point! Indeed it can take forever to mine another block with the difficulty that was set before the event, let alone something around 2,000 blocks. So, I think then we can only hope that some ASICs will survive the catastrophe and hence the needed 2016 blocks will be eventually mined, maybe not in two weeks but in 20 weeks, but still. Another possibility would be a manual retargeting, but I'm not sure if that is technically possible.
Also this
A single retarget never changes the target by more than a factor of 4 either way to prevent large changes in difficulty.
can be a problem if manual adjustment is out of question.
