In my opinion that if hash rate Drops to 50% than A market could crash but hard for sometime but also this hash rate could again go to spike cause miners are all over the world and these miners cannot shut down in a single time frame.
As we know that in a single country that is possible cause if china holds 50% miners tha 20 to 25% has rate can be dropped for manipulation and that happened in 2020. And that's not just new.