It may not disappear, you can find it on CMC if it has been listed on this platform before. It may have been removed from the exchange because of low liquidity levels for a long time, so it removed from the exchange. You can go through telegram of the group to contact the manager to ask for detailed information about your question, hoping you find the answer soon.
when the demand of the tokens falls automatically listed sites will through that coin out of their site.
When there is spam here on the forum you will find the trashcanned policy as well as listing site also do this activity for avoiding the spam coins in their sites.
Please be aware which coin's demand is falling and do not invest on such coins. It will wasted your money.