If Bitcoin's mining difficulty would ever go down it won't be because of Bitcoin's price crashing but because of the mining farms being forced to shutdown which already have taken place in a lot of Chinese Bitcoin miners because of their situation with the COVID 19 but looking at both the difficulty and hashrate Bitcoin has currently you will see that it's not yet falling but maybe if miners from other countries will be affected and their operations will also shutdown I think this will be the start where both will fall down gradually.