I think it depends on the exchanger site. Because I'm always leaving my altcoins in c-cex but it never lost. It would be better if you will leave your bitcoins or altcoins in some legit exchangers like c-cex and yobit to be sure that your bitcoin or altcoin would never be lost or get stolen maybe.
it's not a nice way in my opinion. is better to use an exchange only. then you can sell altcoin when prices are high.
because if it continues silenced then altcoin may have a very low price. grab the opportunity to earn better profits.