People taking out their funds from those exchanges will probably want to do so, often, by cashing out, so as long as these exchanges operate, they will force some downward pressure on the price (though the initial panic selling wave seems to have past a couple of days ago). Once the exchanges close, the downward pressure will disappear, as other entities continue to operate normally and absorb the temporary surplus of supply.
if these users sell on the exchanges because of panic sell and then cash out the fiat then there will not be any additional "surplus of supply" on any other exchange!
instead there will be a recovery because of the huge drop and then because of that recovery (which is a price rise) there will be a lot of FOMO and all those who sold prior to this will start FOMO buying with the money in hand.
