It is impossible for all exchanges to remain in operation. Exchanges thrive on profit from listing new coins/tokens trades and withdrawals. If the volume of trades on the exchange is low, the exchange will start running at a loss. This is the major reason why many are going under: low volume of trades due to bearish market.
Exchange is always alive when the coins that are being listed over there is alive too, that is the reason why sometimes they remove unactive coin due to for them to create space for new coins that has potential and has a better people who supported it. We need to realize that exchange is just an only exchange waiting for alts to come back.