I don't agree. As long as exchange users benefit from tokens, it will not be worthless and will attract other exchanges users to it for more profits. As a BNB holder, you directly benefit from the profits binance makes. Because profits from the exchange are used to burn coins, this creates a basic supply/demand incentive.
If there were only 100 BNB tokens left, and binance made $10 million dollars for the quarter, they would spend $100,000 to buy back and burn each coin. Obviously a lot of people will hold, so the value will keep increasing and attracts more investors. I am a BNB maximalist, and i regret selling my $10,000 BNB into shitcoins and now building back my pile. But sadly shitcoins all fell on average over 90% while BNB is about to hit new highs soon.
OP is talking about what if that exchange completely shuts down or lose their reputation after years? If that means those exchange's tokens might not have any value right.
I think it is worth thinking about but BNB is not in the same level with other coins and most exchanges in the feat of binance dont just quit the business. Binance is so progressive that scare most exchanges with large volume trade but sometimes I think the exchange coin can't be has profitable as bitcoin when use as reward and sorts, bitcoin looks to be most consistently volatile coin..