But if an exchange goes through a hard period of time and shuts downs then ultimately that token will come to its end because there is no community other than that exchange supporting the token simply because it has no usage outside the exchange.
According to me exchanges should promote the usage of their coins/tokens outside the exchange to build a community in support of it. If your community consists of huge individual entities who believe you then a great community can be formed. Otherwise lack of applications would lead these things to disaster.
Exchanges must not just promote their tokens or coins to public but also their own exchange as well because I do believe that before an exchange releases its own coin in the market, it must have first establish its strong position in the public wherein it has a high credibility standard to attract traders to get into their exchange and at the same time know their token so that they could be hitting two birds in one stone in a sense that they have been known through their good aspects as an exchange and at the same time let the people know about their own token. I believe as long as the credibility stands within the exchange, people will surely get along with it and the exchange will never fall out of people's attention so their exchange will keep working or operating same as with their tokens as well in the market.