Nobody can tell if exchanger will not really lets users from trading if the price jumps to much because it has not happened before so no one knows it yet. But in my opinion in case that big pump happen exchanger will still let users to sell or transact their Bitcoin because they don't know if after that big pump there is also a big dump. That's the gamble the exchanger needs to risk if that happens.
Why would the exchange halt the transaction if there is a price pump ,hope you are talking without understand how things work ,as long as there are traders willing to purchase bitcoin at that rate you would sell it ,the exchanges wont halt your transactions and if they do,you could take legal actions against them.So there is no gamble here and the exchange wont be loosing anything if the price of bitcoin rises.
Well significantly these exchangers really benefited this bigger pump and it actually depends on the amounts that has been transact. Actually those who pumped their dumps could exactly have their benefits, but those who gamble their new investment losses it while they buy their bitcoin during the time of massive dumps. But if there's another pump of btc price I think no one loses, but still the price is much expensive to those who recently buy bitcoins to be invested on their wallets.