of course there are miners who will leave whenever price drops but i don't believe it is this drastic to cause any worries, specifically when we see hashrate goes back up without price going back up first.
i am not a fan of conspiracy theories but the reason for such hashrate drops during a price (specially when they don't make sense and then jump back up again) could be a big miner trying to manipulate things and force small miners to exit and push the difficulty down before they come back themselves and mine at a lower difficulty.
It depends on what is a radical change for you. There are owners of Bitcoin who make dozens of payments every day. In case of a significant increase in the mining time of a single block, commissions will also significantly increase, which will hit very hard those who make a lot of payments in Bitcoins every day. This is certainly not fatal, since it will be temporary, but people will either have to wait or incur additional costs.