Let's assume we lose almost all the rest of the miners. What's the longest time that can pass until the next difficulty adjustment?
We can't really have a discussion unless you give actual numbers. The longest time it can take is infinite, with 0 miners.

Don't know if that really answers your question or not.
I'm sorry if "almost all" means 0 to you. Let me try some easier questions for you.
The FAQ states:
it can lower difficulty 400% in 12 hours
First, what does 400% lower difficulty mean given a current difficulty of 18,246?
Why hasn't the difficulty lowered in the last 13+ hours?
I'm not sure why CoinHunter keeps on using this 400% number. It makes absolute no sense. You can't lower a number by 400%. If you lower by 100%, you get 0. Lowering by 400% gives you -54,738?!? I think what he's trying to say is that it can lower at most 75%. Also the 12 hours is an estimate. The actual time depends on how long it takes to find 240 blocks. At the ideal rate of a block every 3 minutes, you will find 240 blocks in 12 hours. But if you lose 90% of your miners, it could take 5 days. And when the difficulty adjusts after 5 days, it will only reduce by 75% max and not 90%.
So, CoinHunter, please fix the text on your website.