I have already experienced such a scenario and honestly, you can't do anything about it when you want to get back your coins from their exchanges because they completely stop the flow of withdrawal and you don't have any other choice but to wait for them to open it back. You can search it on YouTube when Okex has closed their withdrawal in the past and while my XRP is inside their exchange, there are lots of FUDS going on around in the social media where you can read that they will never come back again which is frustrating because I have lots of money in their exchange.
I had such experience with Yobit and Poloniex in the past even though the stuck amount was about hundreds still they can't force you to keep the tokens/coins forever in there but if there is any trading pair opens for the coin that has been closed for the withdrawal then never hesitate even though if the selling price is low than you expected then you may able to get something instead of waiting along with frustrated mindset.